Channel access method for carrying out transmission in unlicensed band, and device using same

ABSTRACT

Disclosed are wireless communication system base stations. Each wireless communication base station comprises a communication module and a processor. When the base stations carry out DRS- and nonunicast data-multiplexed transmission, the processors select one channel access type among two channel access types according to whether both of two conditions are satisfied, the two conditions being that the duration of the DRS- and nonunicast data-multiplexed transmission is 1 ms or less, and the duty cycle of DRS transmission is 1/20 or less. Among the two channel access types, the first type is channel access in which random backoff is carried out using a variable-size contention window (CW), the size of the CW being determined according to channel access priority class; and the second type is channel access in which only single time interval-based LBT is carried out.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system.Specifically, the present disclosure relates to a channel access methodfor transmission including a discovery reference signal anduplink/downlink transmission in a wireless communication systemoperating in an unlicensed band, and a device using same.

BACKGROUND ART

After commercialization of 4th generation (4G) communication system, inorder to meet the increasing demand for wireless data traffic, effortsare being made to develop new 5th generation (5G) communication systems.The 5G communication system is called as a beyond 4G networkcommunication system, a post LTE system, or a new radio (NR) system. Inorder to achieve a high data transfer rate, 5G communication systemsinclude systems operated using the millimeter wave (mmWave) band of 6GHz or more, and include a communication system operated using afrequency band of 6 GHz or less in terms of ensuring coverage so thatimplementations in base stations and terminals are under consideration.

A 3rd generation partnership project (3GPP) NR system enhances spectralefficiency of a network and enables a communication provider to providemore data and voice services over a given bandwidth. Accordingly, the3GPP NR system is designed to meet the demands for high-speed data andmedia transmission in addition to supports for large volumes of voice.The advantages of the NR system are to have a higher throughput and alower latency in an identical platform, support for frequency divisionduplex (FDD) and time division duplex (TDD), and a low operation costwith an enhanced end-user environment and a simple architecture.

For more efficient data processing, dynamic TDD of the NR system may usea method for varying the number of orthogonal frequency divisionmultiplexing (OFDM) symbols that may be used in an uplink and downlinkaccording to data traffic directions of cell users. For example, whenthe downlink traffic of the cell is larger than the uplink traffic, thebase station may allocate a plurality of downlink OFDM symbols to a slot(or subframe). Information about the slot configuration should betransmitted to the terminals.

In order to alleviate the path loss of radio waves and increase thetransmission distance of radio waves in the mmWave band, in 5Gcommunication systems, beamforming, massive multiple input/output(massive MIMO), full dimensional MIMO (FD-MIMO), array antenna, analogbeam-forming, hybrid beamforming that combines analog beamforming anddigital beamforming, and large scale antenna technologies are discussed.In addition, for network improvement of the system, in the 5Gcommunication system, technology developments related to evolved smallcells, advanced small cells, cloud radio access network (cloud RAN),ultra-dense network, device to device communication (D2D), vehicle toeverything communication (V2X), wireless backhaul, non-terrestrialnetwork communication (NTN), moving network, cooperative communication,coordinated multi-points (CoMP), interference cancellation, and the likeare being made. In addition, in the 5G system, hybrid FSK and QAMmodulation (FQAM) and sliding window superposition coding (SWSC), whichare advanced coding modulation (ACM) schemes, and filter bankmulti-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparsecode multiple access (SCMA), which are advanced connectivitytechnologies, are being developed.

Meanwhile, in a human-centric connection network where humans generateand consume information, the Internet has evolved into the Internet ofThings (IoT) network, which exchanges information among distributedcomponents such as objects. Internet of Everything (IoE) technology,which combines IoT technology with big data processing technologythrough connection with cloud servers, is also emerging. In order toimplement IoT, technology elements such as sensing technology,wired/wireless communication and network infrastructure, serviceinterface technology, and security technology are required, so that inrecent years, technologies such as sensor network, machine to machine(M2M), and machine type communication (MTC) have been studied forconnection between objects. In the IoT environment, an intelligentinternet technology (IT) service that collects and analyzes datagenerated from connected objects to create new value in human life canbe provided. Through the fusion and mixture of existing informationtechnology (IT) and various industries, IoT can be applied to fieldssuch as smart home, smart building, smart city, smart car or connectedcar, smart grid, healthcare, smart home appliance, and advanced medicalservice.

Accordingly, various attempts have been made to apply the 5Gcommunication system to the IoT network. For example, technologies suchas a sensor network, a machine to machine (M2M), and a machine typecommunication (MTC) are implemented by techniques such as beamforming,MIMO, and array antennas. The application of the cloud RAN as the bigdata processing technology described above is an example of the fusionof 5G technology and IoT technology. Generally, a mobile communicationsystem has been developed to provide voice service while ensuring theuser's activity.

However, the mobile communication system is gradually expanding not onlythe voice but also the data service, and now it has developed to theextent of providing high-speed data service. However, in a mobilecommunication system in which services are currently being provided, amore advanced mobile communication system is required due to a shortagephenomenon of resources and a high-speed service demand of users.

In recent years, with the explosion of mobile traffic due to the spreadof smart devices, it is becoming difficult to cope with the increasingdata usage for providing cellular communication services using only theexisting licensed frequency spectrums or licensed frequency bands.

In such a situation, a method of using an unlicensed frequency spectrumor an unlicensed frequency band (e.g., 2.4 GHz band, 5 GHz band orhigher band, or the like) for providing cellular communication servicesis being discussed as a solution to the problem of lack of spectrum.

Unlike in licensed bands in which telecommunications carriers secureexclusive use rights through procedures such as auctions, in unlicensedbands, multiple communication devices may be used simultaneously withoutrestrictions on the condition that only a certain level of adjacent bandprotection regulations are observed. For this reason, when an unlicensedband is used for cellular communication service, it is difficult toguarantee the communication quality to the level provided in thelicensed band, and it is likely that interference with existing wirelesscommunication devices (e.g., wireless LAN devices) using the unlicensedband occurs.

In order to use LTE and NR technologies in unlicensed bands, research oncoexistence with existing devices for unlicensed bands and efficientsharing of wireless channels is to be conducted in advance. That is, itis required to develop a robust coexistence mechanism (RCM) such thatdevices using LTE and NR technologies in the unlicensed band do notaffect the existing devices for unlicensed bands.

DISCLOSURE Technical Problem

An embodiment of the present disclosure provides a channel access methodfor performing uplink/downlink transmission in a wireless communicationsystem operating in an unlicensed band, and a device using same.

Technical Solution

A base station of a wireless communication system according to anembodiment of the present disclosure includes: a communication module;and a processor configured to control the communication module. When thebase station performs transmission of a DRS and non-unicast data whichare multiplexed, the processor is configured to select one of twochannel access types according to whether both of two conditions aresatisfied, the two conditions being that a duration of the transmissionof a DRS and non-unicast data which are multiplexed is 1 ms or less, andthat a duty cycle of DRS transmission is 1/20 or less. Among the twochannel access types, a first type is a channel access in which a randombackoff is performed using a variable-size contention window (CW), and asize of the CW is determined according to a channel access priorityclass, and a second type is a channel access in which only LBT based ona single time interval is performed.

When the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, the processor may be configured toperform a channel access employing the first type in order to performthe transmission of a DRS and non-unicast data which are multiplexed.

When the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, the processor may be configured torandomly select a channel access priority class, and apply the selectedchannel access priority class to the channel access employing the firsttype.

When the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, the processor may be configured to:randomly select one of channel access priority classes allowed accordingto a length of the duration of the transmission of a DRS and non-unicastdata which are multiplexed, and apply the selected channel accesspriority class to the channel access employing the first type.

When the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, the processor may be configured toapply, to the channel access employing the first type, a channel accesspriority class having a highest priority.

When the base station performs the transmission of a DRS and non-unicastdata which are multiplexed, through a channel access employing the firsttype, the processor may be configured to adjust the size of the CW,based on a hybrid automatic repeat request (HARQ)-ACK feedback relatedto transmission associated with the channel access priority classdetermining the size of the CW. When the base station is unable todetermine a HARQ-ACK feedback related to transmission associated withthe channel access priority class determining the size of the CW, theprocessor may be configured to perform the channel access employing thefirst type by using a smallest value among CW size values allowed forthe channel access priority class determining the size of the CW.

When the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is 1 ms or shorter, or the duty cycle of the DRStransmission is 1/20 or less, the processor may perform a channel accessusing the second type in order to perform the transmission of a DRS andnon-unicast data which are multiplexed.

A duration of the single time interval may be 25 μs.

The non-unicast data may include at least one of an RACH message-4, ahandover command, a group common PDCCH, a short paging message, othersystem information (OSI), and a random access response (RAR).

A operation method of a base station in a wireless communication systemaccording to an embodiment of the present disclosure includes: when thebase station performs transmission of a DRS and non-unicast data whichare multiplexed, selecting one of two channel access types according towhether both of two conditions are satisfied, the two conditions beingthat a duration of the transmission of a DRS and non-unicast data whichare multiplexed is 1 ms or shorter, and that a duty cycle of DRStransmission is 1/20 or less; and performing the transmission accordingto the selected channel access type. Among the two channel access types,a first type is a channel access in which a random backoff is performedusing a variable-size contention window (CW), and a size of the CW isdetermined according to a channel access priority class, and a secondtype is a channel access in which only LBT based on a single timeinterval is performed.

The performing the transmission may further include, when the durationof the transmission of a DRS and non-unicast data which are multiplexedis longer than 1 ms, or the duty cycle of the DRS transmission is largerthan 1/20, performing a channel access employing the first type in orderto perform the transmission of a DRS and non-unicast data which aremultiplexed.

The performing the channel access employing the first type may include:when the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, randomly selecting a channel accesspriority class; and applying the selected channel access priority classto the channel access employing the first type.

The random selecting the channel access priority class may include, whenthe duration of the transmission of a DRS and non-unicast data which aremultiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, randomly selecting one of channelaccess priority classes allowed according to a length of the duration ofthe transmission of a DRS and non-unicast data which are multiplexed.

The random selecting the channel access priority class may include, whenthe duration of the transmission of a DRS and non-unicast data which aremultiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, applying, by a processor and to achannel access employing the first type, the channel access priorityclass having a highest priority.

The performing the transmission may include: if the base stationperforms transmission of a DRS and non-unicast data which aremultiplexed, through a channel access employing the first type,adjusting the size of the CW, based on a hybrid automatic repeat request(HARQ)-ACK feedback related to transmission associated with the channelaccess priority class determining the size of the CW; and when the basestation is unable to determine a HARQ-ACK feedback related totransmission associated with the channel access priority classdetermining the size of the CW, performing the channel access employingthe first type by using a smallest value among CW size values allowedfor the channel access priority class determining the size of the CW.

The performing the transmission may include, when the duration of thetransmission of a DRS and non-unicast data which are multiplexed is 1 msor shorter, or the duty cycle of the DRS transmission is 1/20 or less,performing a channel access using the second type in order to performthe transmission of a DRS and non-unicast data which are multiplexed.

A duration of the single time interval may be 25 μs.

The non-unicast data may include at least one of an RACH message-4, ahandover command, a group common PDCCH, a short paging message, othersystem information (OSI), and a random access response (RAR).

Advantageous Effects

An embodiment of the present disclosure provides a channel access methodfor transmission including a discovery reference signal in a wirelesscommunication system operating in an unlicensed band, and a device usingsame.

Effects which can be acquired by the present disclosure are not limitedto the effects described above, and other effects that have not beenmentioned may be clearly understood by those skilled in the art from thefollowing description.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a wireless frame structure used in awireless communication system.

FIG. 2 illustrates an example of a downlink (DL)/uplink (UL) slotstructure in a wireless communication system.

FIG. 3 is a diagram for explaining a physical channel used in a 3GPPsystem and a typical signal transmission method using the physicalchannel.

FIG. 4 illustrates an SS/PBCH block for initial cell access in a 3GPP NRsystem.

FIG. 5 illustrates a procedure for transmitting control information anda control channel in a 3GPP NR system.

FIG. 6 illustrates a control resource set (CORESET) in which a physicaldownlink control channel (PUCCH) may be transmitted in a 3GPP NR system.

FIG. 7 illustrates a method for configuring a PDCCH search space in a3GPP NR system.

FIG. 8 is a conceptual diagram illustrating carrier aggregation.

FIG. 9 is a diagram for explaining single carrier communication andmultiple carrier communication.

FIG. 10 is a diagram showing an example in which a cross carrierscheduling technique is applied.

FIG. 11 illustrates a code block group (CBG) configuration and timefrequency resource mapping thereof according to an embodiment of thepresent invention.

FIG. 12 illustrates a procedure in which a base station performs aTB-based transmission or a CBG-based transmission, and a UE transmits aHARQ-ACK in response thereto, according to an embodiment of the presentinvention.

FIG. 13 illustrates a New Radio-Unlicensed (NR-U) service environment.

FIG. 14 illustrates an embodiment of an arrangement scenario of a UE anda base station in an NR-U service environment.

FIG. 15 illustrates a communication method (e.g., wireless LAN)operating in an existing unlicensed band.

FIG. 16 illustrates a channel access procedure based on Category 4 LBTaccording to an embodiment of the present invention.

FIG. 17 illustrates an embodiment of a method of adjusting a contentionwindow size (CWS) based on HARQ-ACK feedback.

FIG. 18 is a block diagram illustrating configurations of a UE and abase station according to an embodiment of the present invention.

FIG. 19 shows the position of OFDM symbols occupied by an SSB accordingto an embodiment of the present disclosure in a slot including 16 OFDMsymbols.

MODE FOR CARRYING OUT THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used as possible by considering functions in the presentinvention, but the terms may be changed depending on an intention ofthose skilled in the art, customs, and emergence of new technology.Further, in a specific case, there is a term arbitrarily selected by anapplicant and in this case, a meaning thereof will be described in acorresponding description part of the invention. Accordingly, it intendsto be revealed that a term used in the specification should be analyzedbased on not just a name of the term but a substantial meaning of theterm and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “connected” to another element, the elementmay be “directly connected” to the other element or “electricallyconnected” to the other element through a third element. Further, unlessexplicitly described to the contrary, the word “comprise” will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements unless otherwise stated. Moreover,limitations such as “more than or equal to” or “less than or equal to”based on a specific threshold may be appropriately substituted with“more than” or “less than”, respectively, in some exemplary embodiments.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), and the like. The CDMA may be implemented by a wirelesstechnology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA may be implemented by a wireless technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMAmay be implemented by a wireless technology such as IEEE 802.11(Wi-Fi),IEEE 802.16(WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) and LTE-advanced (A) is an evolvedversion of the 3GPP LTE. 3GPP new radio (NR) is a system designedseparately from LTE/LTE-A, and is a system for supporting enhancedmobile broadband (eMBB), ultra-reliable and low latency communication(URLLC), and massive machine type communication (mMTC) services, whichare requirements of IMT-2020. For the clear description, 3GPP NR ismainly described, but the technical idea of the present invention is notlimited thereto.

Unless otherwise specified in the present specification, a base stationmay include a next generation node B (gNB) defined in 3GPP NR. Inaddition, unless otherwise specified, the terminal may include userequipment (UE). Hereinafter, in order to help understanding thedescription, each content is divided into embodiments and described, butthe respective embodiments may be used in combination with each other.In the present disclosure, the configuration of the terminal mayindicate configuration by the base station. Specifically, the basestation may transmit a channel or signal to the terminal to set anoperation of the terminal or a parameter value used in a wirelesscommunication system.

FIG. 1 illustrates an example of a wireless frame structure used in awireless communication system.

Referring to FIG. 1, the wireless frame (or radio frame) used in the3GPP NR system may have a length of 10 ms (Δf_(max)N_(f)/100)*T_(c)). Inaddition, the wireless frame includes 10 subframes (SFs) having equalsizes. Herein, Δf_(max)=480*10³ Hz, N_(f)=4096,T_(c)=1/(Δf_(ref)*N_(f,ref)), Δf_(ref)=15*10³ Hz, and N_(f,ref)=2048.Numbers from 0 to 9 may be respectively allocated to 10 subframes withinone wireless frame. Each subframe has a length of 1 ms and may includeone or more slots according to a subcarrier spacing. More specifically,in the 3GPP NR system, the subcarrier spacing that may be used is15*2^(μ) kHz, and μ can have a value of μ=0, 1, 2, 3, 4 as subcarrierspacing configuration. That is, 15 kHz, 30 kHz, 60 kHz, 120 kHz and 240kHz may be used for subcarrier spacing. One subframe having a length of1 ms may include 2^(μ) slots. In this case, the length of each slot is2^(−μ) ms. Numbers from 0 to 2^(μ)−1 may be respectively allocated to2^(μ) slots within one wireless frame. In addition, numbers from 0 to10*2^(μ)−1 may be respectively allocated to slots within one subframe.The time resource may be distinguished by at least one of a wirelessframe number (also referred to as a wireless frame index), a subframenumber (also referred to as a subframe index), and a slot number (or aslot index).

FIG. 2 illustrates an example of a downlink (DL)/uplink (UL) slotstructure in a wireless communication system. In particular, FIG. 2shows the structure of the resource grid of the 3GPP NR system.

There is one resource grid per antenna port. Referring to FIG. 2, a slotincludes a plurality of orthogonal frequency division multiplexing(OFDM) symbols in a time domain and includes a plurality of resourceblocks (RBs) in a frequency domain. An OFDM symbol also means one symbolsection. Unless otherwise specified, OFDM symbols may be referred tosimply as symbols. One RB includes 12 consecutive subcarriers in thefrequency domain. Referring to FIG. 2, a signal transmitted from eachslot may be represented by a resource grid including N^(size,μ)_(grid,x)*N^(RB) _(sc) subcarriers, and N^(slot) _(symb) OFDM symbols.Here, x=DL when the signal is a DL signal, and x=UL when the signal isan UL signal. N^(size,μ) _(grid,x) represents the number of resourceblocks (RBs) according to the subcarrier spacing constituent ρ (x is DLor UL), and N^(slot) _(symb) represents the number of OFDM symbols in aslot. N^(RB) _(sc) is the number of subcarriers constituting one RB andN^(RB) _(sc)=12. An OFDM symbol may be referred to as a cyclic shiftOFDM (CP-OFDM) symbol or a discrete Fourier transform spread OFDM(DFT-s-OFDM) symbol according to a multiple access scheme.

The number of OFDM symbols included in one slot may vary according tothe length of a cyclic prefix (CP). For example, in the case of a normalCP, one slot includes 14 OFDM symbols, but in the case of an extendedCP, one slot may include 12 OFDM symbols. In a specific embodiment, theextended CP can only be used at 60 kHz subcarrier spacing. In FIG. 2,for convenience of description, one slot is configured with 14 OFDMsymbols by way of example, but embodiments of the present disclosure maybe applied in a similar manner to a slot having a different number ofOFDM symbols. Referring to FIG. 2, each OFDM symbol includes N^(size,μ)_(grid,x)*N^(RB) _(sc) subcarriers in the frequency domain. The type ofsubcarrier may be divided into a data subcarrier for data transmission,a reference signal subcarrier for transmission of a reference signal,and a guard band. The carrier frequency is also referred to as thecenter frequency (fc).

One RB may be defined by N^(RB) _(sc) (e.g., 12) consecutive subcarriersin the frequency domain. For reference, a resource configured with oneOFDM symbol and one subcarrier may be referred to as a resource element(RE) or a tone. Therefore, one RB can be configured with N^(slot)_(symb)*N^(RB) _(sc) resource elements. Each resource element in theresource grid can be uniquely defined by a pair of indexes (k, l) in oneslot. k may be an index assigned from 0 to N^(size,μ) _(grid, x)*N^(RB)_(sc)−1 in the frequency domain, and l may be an index assigned from 0to N^(slot) _(symb)−1 in the time domain.

In order for the UE to receive a signal from the base station or totransmit a signal to the base station, the time/frequency of the UE maybe synchronized with the time/frequency of the base station. This isbecause when the base station and the UE are synchronized, the UE candetermine the time and frequency parameters necessary for demodulatingthe DL signal and transmitting the UL signal at the correct time.

Each symbol of a radio frame used in a time division duplex (TDD) or anunpaired spectrum may be configured with at least one of a DL symbol, anUL symbol, and a flexible symbol. A radio frame used as a DL carrier ina frequency division duplex (FDD) or a paired spectrum may be configuredwith a DL symbol or a flexible symbol, and a radio frame used as a ULcarrier may be configured with a UL symbol or a flexible symbol. In theDL symbol, DL transmission is possible, but UL transmission isimpossible. In the UL symbol, UL transmission is possible, but DLtransmission is impossible. The flexible symbol may be determined to beused as a DL or an UL according to a signal.

Information on the type of each symbol, i.e., information representingany one of DL symbols, UL symbols, and flexible symbols, may beconfigured with a cell-specific or common radio resource control (RRC)signal. In addition, information on the type of each symbol mayadditionally be configured with a UE-specific or dedicated RRC signal.The base station informs, by using cell-specific RRC signals, i) theperiod of cell-specific slot configuration, ii) the number of slots withonly DL symbols from the beginning of the period of cell-specific slotconfiguration, iii) the number of DL symbols from the first symbol ofthe slot immediately following the slot with only DL symbols, iv) thenumber of slots with only UL symbols from the end of the period of cellspecific slot configuration, and v) the number of UL symbols from thelast symbol of the slot immediately before the slot with only the ULsymbol. Here, symbols not configured with any one of a UL symbol and aDL symbol are flexible symbols.

When the information on the symbol type is configured with theUE-specific RRC signal, the base station may signal whether the flexiblesymbol is a DL symbol or an UL symbol in the cell-specific RRC signal.In this case, the UE-specific RRC signal can not change a DL symbol or aUL symbol configured with the cell-specific RRC signal into anothersymbol type. The UE-specific RRC signal may signal the number of DLsymbols among the N^(slot) _(symb) symbols of the corresponding slot foreach slot, and the number of UL symbols among the N^(slot) _(symb)symbols of the corresponding slot. In this case, the DL symbol of theslot may be continuously configured with the first symbol to the i-thsymbol of the slot. In addition, the UL symbol of the slot may becontinuously configured with the j-th symbol to the last symbol of theslot (where i<j). In the slot, symbols not configured with any one of aUL symbol and a DL symbol are flexible symbols.

The type of symbol configured with the above RRC signal may be referredto as a semi-static DL/UL configuration. In the semi-static DL/ULconfiguration previously configured with RRC signals, the flexiblesymbol may be indicated as a DL symbol, an UL symbol, or a flexiblesymbol through dynamic slot format information (SFI) transmitted on aphysical DL control channel (PDCCH). In this case, the DL symbol or ULsymbol configured with the RRC signal is not changed to another symboltype. Table 1 exemplifies the dynamic SFI that the base station canindicate to the UE.

TABLE 1 Symbol number in a slot Index 0 1 2 3 4 5 6 7 8 9 10 11 12 13  0D D D D D D D D D D D D D D  1 U U U U U U U U U U U U U U  2 X X X X XX X X X X X X X X  3 D D D D D D D D D D D D D X  4 D D D D D D D D D DD D X X  5 D D D D D D D D D D D X X X  6 D D D D D D D D D D X X X X  7D D D D D D D D D X X X X X  8 X X X X X X X X X X X X X U  9 X X X X XX X X X X X X U U  10 X U U U U U U U U U U U U U  11 X X U U U U U U UU U U U U  12 X X X U U U U U U U U U U U  13 X X X X U U U U U U U U UU  14 X X X X X U U U U U U U U U  15 X X X X X X U U U U U U U U  16 DX X X X X X X X X X X X X  17 D D X X X X X X X X X X X X  18 D D D X XX X X X X X X X X  19 D X X X X X X X X X X X X U  20 D D X X X X X X XX X X X U  21 D D D X X X X X X X X X X U  22 D X X X X X X X X X X X UU  23 D D X X X X X X X X X X U U  24 D D D X X X X X X X X X U U  25 DX X X X X X X X X X U U U  26 D D X X X X X X X X X U U U  27 D D D X XX X X X X X U U U  28 D D D D D D D D D D D D X U  29 D D D D D D D D DD D X X U  30 D D D D D D D D D D X X X U  31 D D D D D D D D D D D X UU  32 D D D D D D D D D D X X U U  33 D D D D D D D D D X X X U U  34 DX U U U U U U U U U U U U  35 D D X U U U U U U U U U U U  36 D D D X UU U U U U U U U U  37 D X X U U U U U U U U U U U  38 D D X X U U U U UU U U U U  39 D D D X X U U U U U U U U U  40 D X X X U U U U U U U U UU  41 D D X X X U U U U U U U U U  42 D D D X X X U U U U U U U U  43 DD D D D D D D D X X X X U  44 D D D D D D X X X X X X U U  45 D D D D DD X X U U U U U U  46 D D D D D X U D D D D D X U  47 D D X U U U U D DX U U U U  48 D X U U U U U D X U U U U U  49 D D D D X X U D D D D X XU  50 D D X X U U U D D X X U U U  51 D X X U U U U D X X U U U U  52 DX X X X X U D X X X X X U  53 D D X X X X U D D X X X X U  54 X X X X XX X D D D D D D D  55 D D X X X U U U D D D D D D  56- Reserved 266

In Table 1, D denotes a DL symbol, U denotes a UL symbol, and X denotesa flexible symbol. As shown in Table 1, up to two DL/UL switching in oneslot may be allowed.

FIG. 3 is a diagram for explaining a physical channel used in a 3GPPsystem (e.g., NR) and a typical signal transmission method using thephysical channel.

If the power of the UE is turned on or the UE camps on a new cell, theUE performs an initial cell search (step S101). Specifically, the UE maysynchronize with the BS in the initial cell search. For this, the UE mayreceive a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS) from the base station to synchronize withthe base station, and obtain information such as a cell ID. Thereafter,the UE can receive the physical broadcast channel from the base stationand obtain the broadcast information in the cell.

Upon completion of the initial cell search, the UE receives a physicaldownlink shared channel (PDSCH) according to the physical downlinkcontrol channel (PDCCH) and information in the PDCCH, so that the UE canobtain more specific system information than the system informationobtained through the initial cell search (step S102). Herein, the systeminformation received by the UE is cell-common system information fornormal operating of the UE in a physical layer in radio resource control(RRC) and is referred to remaining system information, or systeminformation block (SIB) 1 is called.

When the UE initially accesses the base station or does not have radioresources for signal transmission (i.e. the UE at RRC_IDLE mode), the UEmay perform a random access procedure on the base station (steps S103 toS106). First, the UE can transmit a preamble through a physical randomaccess channel (PRACH) (step S103) and receive a response message forthe preamble from the base station through the PDCCH and thecorresponding PDSCH (step S104). When a valid random access responsemessage is received by the UE, the UE transmits data including theidentifier of the UE and the like to the base station through a physicaluplink shared channel (PUSCH) indicated by the UL grant transmittedthrough the PDCCH from the base station (step S105). Next, the UE waitsfor reception of the PDCCH as an indication of the base station forcollision resolution. If the UE successfully receives the PDCCH throughthe identifier of the UE (step S106), the random access process isterminated. The UE may obtain UE-specific system information for normaloperating of the UE in the physical layer in RRC layer during a randomaccess process. When the UE obtain the UE-specific system information,the UE enter RRC connecting mode (RRC_CONNECTED mode).

The RRC layer is used for generating or managing message for controllingconnection between the UE and radio access network (RAN). In moredetail, the base station and the UE, in the RRC layer, may performbroadcasting cell system information required by every UE in the cell,managing mobility and handover, measurement report of the UE, storagemanagement including UE capability management and device management. Ingeneral, the RRC signal is not changed and maintained quite longinterval since a period of an update of a signal delivered in the RRClayer is longer than a transmission time interval (TTI) in physicallayer.

After the above-described procedure, the UE receives PDCCH/PDSCH (stepS107) and transmits a physical uplink shared channel (PUSCH)/physicaluplink control channel (PUCCH) (step S108) as a general UL/DL signaltransmission procedure. In particular, the UE may receive downlinkcontrol information (DCI) through the PDCCH. The DCI may include controlinformation such as resource allocation information for the UE. Also,the format of the DCI may vary depending on the intended use. The uplinkcontrol information (UCI) that the UE transmits to the base stationthrough UL includes a DL/UL ACK/NACK signal, a channel quality indicator(CQI), a precoding matrix index (PMI), a rank indicator (RI), and thelike. Here, the CQI, PMI, and R777I may be included in channel stateinformation (CSI). In the 3GPP NR system, the UE may transmit controlinformation such as HARQ-ACK and CSI described above through the PUSCHand/or PUCCH.

FIG. 4 illustrates an SS/PBCH block for initial cell access in a 3GPP NRsystem.

When the power is turned on or wanting to access a new cell, the UE mayobtain time and frequency synchronization with the cell and perform aninitial cell search procedure. The UE may detect a physical cellidentity N^(cell) _(ID) of the cell during a cell search procedure. Forthis, the UE may receive a synchronization signal, for example, aprimary synchronization signal (PSS) and a secondary synchronizationsignal (SSS), from a base station, and synchronize with the basestation. In this case, the UE can obtain information such as a cellidentity (ID).

Referring to FIG. 4(a), a synchronization signal (SS) will be describedin more detail. The synchronization signal can be classified into PSSand SSS. The PSS may be used to obtain time domain synchronizationand/or frequency domain synchronization, such as OFDM symbolsynchronization and slot synchronization. The SSS can be used to obtainframe synchronization and cell group ID. Referring to FIG. 4(a) andTable 2, the SS/PBCH block can be configured with consecutive 20 RBs(=240 subcarriers) in the frequency axis, and can be configured withconsecutive 4 OFDM symbols in the time axis. In this case, in theSS/PBCH block, the PSS is transmitted in the first OFDM symbol and theSSS is transmitted in the third OFDM symbol through the 56th to 182thsubcarriers. Here, the lowest subcarrier index of the SS/PBCH block isnumbered from 0. In the first OFDM symbol in which the PSS istransmitted, the base station does not transmit a signal through theremaining subcarriers, i.e., 0th to 55th and 183th to 239th subcarriers.In addition, in the third OFDM symbol in which the SSS is transmitted,the base station does not transmit a signal through 48th to 55th and183th to 191th subcarriers. The base station transmits a physicalbroadcast channel (PBCH) through the remaining RE except for the abovesignal in the SS/PBCH block.

TABLE 2 Subcarrier number k OFDM symbol number/relative relative to theChannel or to the start of an start of an signal SS/PBCH block SS/PBCHblock PSS 0 56, 57, . . . , 182 SSS 2 56, 57, . . . , 182 Set to 0 0 0,1, . . . , 55, 183, 184, . . . , 239 2 48, 49, . . . , 55, 183, 184, . .. , 191 PBCH 1, 3 0, 1, . . . , 239 2 0, 1, . . . , 47, 192, 193, . . ., 239 DM-RS for 1, 3 0 + v, 4 + v, PBCH 8 + v, . . . , 236 + v 2 0 + v,4 + v, 8 + v, . . . , 44 + v, 192 + v, 196 + v, . . . , 236 + v

The SS allows a total of 1008 unique physical layer cell IDs to begrouped into 336 physical-layer cell-identifier groups, each groupincluding three unique identifiers, through a combination of three PSSsand SSSs, specifically, such that each physical layer cell ID is to beonly a part of one physical-layer cell-identifier group. Therefore, thephysical layer cell ID N^(cell) _(ID)=3N⁽¹⁾ _(ID)+N⁽²⁾ _(ID) can beuniquely defined by the index N⁽¹⁾ _(ID) ranging from 0 to 335indicating a physical-layer cell-identifier group and the index N⁽²⁾_(ID) ranging from 0 to 2 indicating a physical-layer identifier in thephysical-layer cell-identifier group. The UE may detect the PSS andidentify one of the three unique physical-layer identifiers. Inaddition, the UE can detect the SSS and identify one of the 336 physicallayer cell IDs associated with the physical-layer identifier. In thiscase, the sequence d_(PSS)(n) of the PSS is as follows.

d _(PSS)(n)=1−2x(m)

m=(n+43N _(ID) ⁽²⁾)mod 127

0≤n<127

Here, x(i+7)=(x(i+4)+x(i))mod 2 and is given as

[x(6) x(5) x(4) x(3) x(2) x(1) x(0)]=[1

Further, the sequence d_(SSS)(n) of the SSS is as follows.

d_(SSS)(n) = [1 − 2x₀((n + m₀)mod 127)][1 − 2x₁((n + m₁)mod 127)]$m_{0} = {{15\left\lfloor \frac{N_{ID}^{(1)}}{112} \right\rfloor} + {5N_{ID}^{(2)}}}$m₁ = N_(ID)⁽¹⁾mod 112 0 ≤ n ≤ 127 x₀(i + 7) = (x₀(i + 4) + x₀(i))mod 2x₁(i + 7) = (x₁(i + 1) + x₁(i))mod 2 Here,

and is given as

[x ₀(6)x ₀(5)x ₀(4)x ₀(3)x ₀(2)x ₀(1)x ₀(0)]=[0 0 0 0 0 0 1]

[x ₁(6)x ₁(5)x ₁(4)x ₁(3)x ₁(2)x ₁(1)x ₁(0)]=[0 0 0 0 0 0 1]

A radio frame with a 10 ms length may be divided into two half frameswith a 5 ms length. Referring to FIG. 4(b), a description will be madeof a slot in which SS/PBCH blocks are transmitted in each half frame. Aslot in which the SS/PBCH block is transmitted may be any one of thecases A, B, C, D, and E. In the case A, the subcarrier spacing is 15 kHzand the starting time point of the SS/PBCH block is the ({2, 8}+14*n)-thsymbol. In this case, n=0 or 1 at a carrier frequency of 3 GHz or less.In addition, it may be n=0, 1, 2, 3 at carrier frequencies above 3 GHzand below 6 GHz. In the case B, the subcarrier spacing is 30 kHz and thestarting time point of the SS/PBCH block is {4, 8, 16, 20}+28*n. In thiscase, n=0 at a carrier frequency of 3 GHz or less. In addition, it maybe n=0, 1 at carrier frequencies above 3 GHz and below 6 GHz. In thecase C, the subcarrier spacing is 30 kHz and the starting time point ofthe SS/PBCH block is the ({2, 8}+14*n)-th symbol. In this case, n=0 or 1at a carrier frequency of 3 GHz or less. In addition, it may be n=0, 1,2, 3 at carrier frequencies above 3 GHz and below 6 GHz. In the case D,the subcarrier spacing is 120 kHz and the starting time point of theSS/PBCH block is the ({4, 8, 16, 20}+28*n)-th symbol. In this case, at acarrier frequency of 6 GHz or more, n=0, 1, 2, 3, 5, 6, 7, 8, 10, 11,12, 13, 15, 16, 17, 18. In the case E, the subcarrier spacing is 240 kHzand the starting time point of the SS/PBCH block is the ({8, 12, 16, 20,32, 36, 40, 44}+56*n)-th symbol. In this case, at a carrier frequency of6 GHz or more, n=0, 1, 2, 3, 5, 6, 7, 8.

FIG. 5 illustrates a procedure for transmitting control information anda control channel in a 3GPP NR system. Referring to FIG. 5(a), the basestation may add a cyclic redundancy check (CRC) masked (e.g., an XORoperation) with a radio network temporary identifier (RNTI) to controlinformation (e.g., downlink control information (DCI)) (step S202). Thebase station may scramble the CRC with an RNTI value determinedaccording to the purpose/target of each control information. The commonRNTI used by one or more UEs can include at least one of a systeminformation RNTI (SI-RNTI), a paging RNTI (P-RNTI), a random access RNTI(RA-RNTI), and a transmit power control RNTI (TPC-RNTI). In addition,the UE-specific RNTI may include at least one of a cell temporary RNTI(C-RNTI), and the CS-RNTI. Thereafter, the base station may performrate-matching (step S206) according to the amount of resource(s) usedfor PDCCH transmission after performing channel encoding (e.g., polarcoding) (step S204). Thereafter, the base station may multiplex theDCI(s) based on the control channel element (CCE) based PDCCH structure(step S208). In addition, the base station may apply an additionalprocess (step S210) such as scrambling, modulation (e.g., QPSK),interleaving, and the like to the multiplexed DCI(s), and then map theDCI(s) to the resource to be transmitted. The CCE is a basic resourceunit for the PDCCH, and one CCE may include a plurality (e.g., six) ofresource element groups (REGs). One REG may be configured with aplurality (e.g., 12) of REs. The number of CCEs used for one PDCCH maybe defined as an aggregation level. In the 3GPP NR system, anaggregation level of 1, 2, 4, 8, or 16 may be used. FIG. 5(b) is adiagram related to a CCE aggregation level and the multiplexing of aPDCCH and illustrates the type of a CCE aggregation level used for onePDCCH and CCE(s) transmitted in the control area according thereto.

FIG. 6 illustrates a control resource set (CORESET) in which a physicaldownlink control channel (PUCCH) may be transmitted in a 3GPP NR system.

The CORESET is a time-frequency resource in which PDCCH, that is, acontrol signal for the UE, is transmitted. In addition, a search spaceto be described later may be mapped to one CORESET. Therefore, the UEmay monitor the time-frequency domain designated as CORESET instead ofmonitoring all frequency bands for PDCCH reception, and decode the PDCCHmapped to CORESET. The base station may configure one or more CORESETsfor each cell to the UE. The CORESET may be configured with up to threeconsecutive symbols on the time axis. In addition, the CORESET may beconfigured in units of six consecutive PRBs on the frequency axis. Inthe embodiment of FIG. 5, CORESET #1 is configured with consecutivePRBs, and CORESET #2 and CORESET #3 are configured with discontinuousPRBs. The CORESET can be located in any symbol in the slot. For example,in the embodiment of FIG. 5, CORESET #1 starts at the first symbol ofthe slot, CORESET #2 starts at the fifth symbol of the slot, and CORESET#9 starts at the ninth symbol of the slot.

FIG. 7 illustrates a method for setting a PUCCH search space in a 3GPPNR system.

In order to transmit the PDCCH to the UE, each CORESET may have at leastone search space. In the embodiment of the present disclosure, thesearch space is a set of all time-frequency resources (hereinafter,PDCCH candidates) through which the PDCCH of the UE is capable of beingtransmitted. The search space may include a common search space that theUE of the 3GPP NR is required to commonly search and a UE-specific or aUE-specific search space that a specific UE is required to search. Inthe common search space, UE may monitor the PDCCH that is set so thatall UEs in the cell belonging to the same base station commonly search.In addition, the UE-specific search space may be set for each UE so thatUEs monitor the PDCCH allocated to each UE at different search spaceposition according to the UE. In the case of the UE-specific searchspace, the search space between the UEs may be partially overlapped andallocated due to the limited control area in which the PDCCH may beallocated. Monitoring the PDCCH includes blind decoding for PDCCHcandidates in the search space. When the blind decoding is successful,it may be expressed that the PDCCH is (successfully) detected/receivedand when the blind decoding fails, it may be expressed that the PDCCH isnot detected/not received, or is not successfully detected/received.

For convenience of explanation, a PDCCH scrambled with a group common(GC) RNTI previously known to one or more UEs so as to transmit DLcontrol information to the one or more UEs is referred to as a groupcommon (GC) PDCCH or a common PDCCH. In addition, a PDCCH scrambled witha specific-terminal RNTI that a specific UE already knows so as totransmit UL scheduling information or DL scheduling information to thespecific UE is referred to as a specific-UE PDCCH. The common PDCCH maybe included in a common search space, and the UE-specific PDCCH may beincluded in a common search space or a UE-specific PDCCH.

The base station may signal each UE or UE group through a PDCCH aboutinformation (i.e., DL Grant) related to resource allocation of a pagingchannel (PCH) and a downlink-shared channel (DL-SCH) that are atransmission channel or information (i.e., UL grant) related to resourceallocation of a uplink-shared channel (UL-SCH) and a hybrid automaticrepeat request (HARD). The base station may transmit the PCH transportblock and the DL-SCH transport block through the PDSCH. The base stationmay transmit data excluding specific control information or specificservice data through the PDSCH. In addition, the UE may receive dataexcluding specific control information or specific service data throughthe PDSCH.

The base station may include, in the PDCCH, information on to which UE(one or a plurality of UEs) PDSCH data is transmitted and how the PDSCHdata is to be received and decoded by the corresponding UE, and transmitthe PDCCH. For example, it is assumed that the DCI transmitted on aspecific PDCCH is CRC masked with an RNTI of “A”, and the DCI indicatesthat PDSCH is allocated to a radio resource (e.g., frequency location)of “B” and indicates transmission format information (e.g., transportblock size, modulation scheme, coding information, etc.) of “C”. The UEmonitors the PDCCH using the RNTI information that the UE has. In thiscase, if there is a UE which performs blind decoding the PDCCH using the“A” RNTI, the UE receives the PDCCH, and receives the PDSCH indicated by“B” and “C” through the received PDCCH information.

Table 3 shows an embodiment of a physical uplink control channel (PUCCH)used in a wireless communication system.

TABLE 3 PUCCH format Length in OFDM symbols Number of bits 0 1-2  ≤2 14-14 ≤2 2 1-2  >2 3 4-14 >2 4 4-14 >2

The PUCCH may be used to transmit the following UL control information(UCI).

-   -   Scheduling Request (SR): Information used for requesting a UL        UL-SCH resource.    -   HARQ-ACK: A Response to PDCCH (indicating DL SPS release) and/or        a response to DL transport block (TB) on PDSCH. HARQ-ACK        indicates whether information successfully transmitted on the        PDCCH or PDSCH is received. The HARQ-ACK response includes        positive ACK (simply ACK), negative ACK (hereinafter NACK),        Discontinuous Transmission (DTX), or NACK/DTX. Here, the term        HARQ-ACK is used mixed with HARQ-ACK/NACK and ACK/NACK. In        general, ACK may be represented by bit value 1 and NACK may be        represented by bit value 0.    -   Channel State Information (CSI): Feedback information on the DL        channel. The UE generates it based on the CSI-Reference Signal        (RS) transmitted by the base station. Multiple Input Multiple        Output (MIMO)-related feedback information includes a Rank        Indicator (RI) and a Precoding Matrix Indicator (PMI). CSI can        be divided into CSI part 1 and CSI part 2 according to the        information indicated by CSI.

In the 3GPP NR system, five PUCCH formats may be used to support variousservice scenarios, various channel environments, and frame structures.

PUCCH format 0 is a format capable of delivering 1-bit or 2-bit HARQ-ACKinformation or SR. PUCCH format 0 can be transmitted through one or twoOFDM symbols on the time axis and one PRB on the frequency axis. WhenPUCCH format 0 is transmitted in two OFDM symbols, the same sequence onthe two symbols may be transmitted through different RBs. In this case,the sequence may be a sequence cyclic shifted (CS) from a base sequenceused in PUCCH format 0. Through this, the UE may obtain a frequencydiversity gain. In more detail, the UE may determine a cyclic shift (CS)value m_(cs) according to M_(bit) bit UCI (M_(bit)=1 or 2). In addition,the base sequence having the length of 12 may be transmitted by mappinga cyclic shifted sequence based on a predetermined CS value m_(cs) toone OFDM symbol and 12 REs of one RB. When the number of cyclic shiftsavailable to the UE is 12 and M_(bit)=1, 1 bit UCI 0 and 1 may be mappedto two cyclic shifted sequences having a difference of 6 in the cyclicshift value, respectively. In addition, when M_(bit)=2, 2 bit UCI 00,01, 11, and 10 may be mapped to four cyclic shifted sequences having adifference of 3 in cyclic shift values, respectively.

PUCCH format 1 may deliver 1-bit or 2-bit HARQ-ACK information or SR.PUCCH format 1 maybe transmitted through consecutive OFDM symbols on thetime axis and one PRB on the frequency axis. Here, the number of OFDMsymbols occupied by PUCCH format 1 may be one of 4 to 14. Morespecifically, UCI, which is M_(bit)=1, may be BPSK-modulated. The UE maymodulate UCI, which is M_(bit)=2, with quadrature phase shift keying(QPSK). A signal is obtained by multiplying a modulated complex valuedsymbol d(0) by a sequence of length 12. In this case, the sequence maybe a base sequence used for PUCCH format 0. The UE spreads theeven-numbered OFDM symbols to which PUCCH format 1 is allocated throughthe time axis orthogonal cover code (OCC) to transmit the obtainedsignal. PUCCH format 1 determines the maximum number of different UEsmultiplexed in the one RB according to the length of the OCC to be used.A demodulation reference signal (DMRS) may be spread with OCC and mappedto the odd-numbered OFDM symbols of PUCCH format 1.

PUCCH format 2 may deliver UCI exceeding 2 bits. PUCCH format 2 may betransmitted through one or two OFDM symbols on the time axis and one ora plurality of RBs on the frequency axis. When PUCCH format 2 istransmitted in two OFDM symbols, the sequences which are transmitted indifferent RBs through the two OFDM symbols may be same each other. Here,the sequence may be a plurality of modulated complex valued symbolsd(0), . . . , d(M_(symbol)−1). Here, M_(symbol) may be M_(bit)/2.Through this, the UE may obtain a frequency diversity gain. Morespecifically, M_(bit) bit UCI (M_(bit)>2) is bit-level scrambled, QPSKmodulated, and mapped to RB(s) of one or two OFDM symbol(s). Here, thenumber of RBs may be one of 1 to 16.

PUCCH format 3 or PUCCH format 4 may deliver UCI exceeding 2 bits. PUCCHformat 3 or PUCCH format 4 may be transmitted through consecutive OFDMsymbols on the time axis and one PRB on the frequency axis. The numberof OFDM symbols occupied by PUCCH format 3 or PUCCH format 4 may be oneof 4 to 14. Specifically, the UE modulates M_(bit) bits UCI (M_(bit)>2)with π/2-Binary Phase Shift Keying (BPSK) or QPSK to generate a complexvalued symbol d(0) to d(M_(symb)−1). Here, when using π/2-BPSK,M_(symb)=M_(bit), and when using QPSK, M_(symb)=M_(bit)/2. The UE maynot apply block-unit spreading to the PUCCH format 3. However, the UEmay apply block-unit spreading to one RB (i.e., 12 subcarriers) usingPreDFT-OCC of a length of 12 such that PUCCH format 4 may have two orfour multiplexing capacities. The UE performs transmit precoding (orDFT-precoding) on the spread signal and maps it to each RE to transmitthe spread signal.

In this case, the number of RBs occupied by PUCCH format 2, PUCCH format3, or PUCCH format 4 may be determined according to the length andmaximum code rate of the UCI transmitted by the UE. When the UE usesPUCCH format 2, the UE may transmit HARQ-ACK information and CSIinformation together through the PUCCH. When the number of RBs that theUE may transmit is greater than the maximum number of RBs that PUCCHformat 2, or PUCCH format 3, or PUCCH format 4 may use, the UE maytransmit only the remaining UCI information without transmitting someUCI information according to the priority of the UCI information.

PUCCH format 1, PUCCH format 3, or PUCCH format 4 may be configuredthrough the RRC signal to indicate frequency hopping in a slot. Whenfrequency hopping is configured, the index of the RB to be frequencyhopped may be configured with an RRC signal. When PUCCH format 1, PUCCHformat 3, or PUCCH format 4 is transmitted through N OFDM symbols on thetime axis, the first hop may have floor (N/2) OFDM symbols and thesecond hop may have ceiling(N/2) OFDM symbols.

PUCCH format 1, PUCCH format 3, or PUCCH format 4 may be configured tobe repeatedly transmitted in a plurality of slots. In this case, thenumber K of slots in which the PUCCH is repeatedly transmitted may beconfigured by the RRC signal. The repeatedly transmitted PUCCHs muststart at an OFDM symbol of the constant position in each slot, and havethe constant length. When one OFDM symbol among OFDM symbols of a slotin which a UE should transmit a PUCCH is indicated as a DL symbol by anRRC signal, the UE may not transmit the PUCCH in a corresponding slotand delay the transmission of the PUCCH to the next slot to transmit thePUCCH.

Meanwhile, in the 3GPP NR system, a UE may performtransmission/reception using a bandwidth equal to or less than thebandwidth of a carrier (or cell). For this, the UE may receive theBandwidth part (BWP) configured with a continuous bandwidth of some ofthe carrier's bandwidth. A UE operating according to TDD or operating inan unpaired spectrum can receive up to four DL/UL BWP pairs in onecarrier (or cell). In addition, the UE may activate one DL/UL BWP pair.A UE operating according to FDD or operating in paired spectrum canreceive up to four DL BWPs on a DL carrier (or cell) and up to four ULBWPs on a UL carrier (or cell). The UE may activate one DL BWP and oneUL BWP for each carrier (or cell). The UE may not perform reception ortransmission in a time-frequency resource other than the activated BWP.The activated BWP may be referred to as an active BWP.

The base station may indicate the activated BWP among the BWPsconfigured by the UE through downlink control information (DCI). The BWPindicated through the DCI is activated and the other configured BWP(s)are deactivated. In a carrier (or cell) operating in TDD, the basestation may include, in the DCI for scheduling PDSCH or PUSCH, abandwidth part indicator (BPI) indicating the BWP to be activated tochange the DL/UL BWP pair of the UE. The UE may receive the DCI forscheduling the PDSCH or PUSCH and may identify the DL/UL BWP pairactivated based on the BPI. For a DL carrier (or cell) operating in anFDD, the base station may include a BPI indicating the BWP to beactivated in the DCI for scheduling PDSCH so as to change the DL BWP ofthe UE. For a UL carrier (or cell) operating in an FDD, the base stationmay include a BPI indicating the BWP to be activated in the DCI forscheduling PUSCH so as to change the UL BWP of the UE.

FIG. 8 is a conceptual diagram illustrating carrier aggregation.

The carrier aggregation is a method in which the UE uses a plurality offrequency blocks or cells (in the logical sense) configured with ULresources (or component carriers) and/or DL resources (or componentcarriers) as one large logical frequency band in order for a wirelesscommunication system to use a wider frequency band. One componentcarrier may also be referred to as a term called a Primary cell (PCell)or a Secondary cell (SCell), or a Primary SCell (PScell). However,hereinafter, for convenience of description, the term “componentcarrier” is used.

Referring to FIG. 8, as an example of a 3GPP NR system, the entiresystem band may include up to 16 component carriers, and each componentcarrier may have a bandwidth of up to 400 MHz. The component carrier mayinclude one or more physically consecutive subcarriers. Although it isshown in FIG. 8 that each of the component carriers has the samebandwidth, this is merely an example, and each component carrier mayhave a different bandwidth. Also, although each component carrier isshown as being adjacent to each other in the frequency axis, thedrawings are shown in a logical concept, and each component carrier maybe physically adjacent to one another, or may be spaced apart.

Different center frequencies may be used for each component carrier.Also, one common center frequency may be used in physically adjacentcomponent carriers. Assuming that all the component carriers arephysically adjacent in the embodiment of FIG. 8, center frequency A maybe used in all the component carriers. Further, assuming that therespective component carriers are not physically adjacent to each other,center frequency A and the center frequency B can be used in each of thecomponent carriers.

When the total system band is extended by carrier aggregation, thefrequency band used for communication with each UE can be defined inunits of a component carrier. UE A may use 100 MHz, which is the totalsystem band, and performs communication using all five componentcarriers. UEs B₁˜B₅ can use only a 20 MHz bandwidth and performcommunication using one component carrier. UEs C₁ and C₂ may use a 40MHz bandwidth and perform communication using two component carriers,respectively. The two component carriers may be logically/physicallyadjacent or non-adjacent. UE C₁ represents the case of using twonon-adjacent component carriers, and UE C₂ represents the case of usingtwo adjacent component carriers.

FIG. 9 is a drawing for explaining single carrier communication andmultiple carrier communication. Particularly, FIG. 9(a) shows a singlecarrier subframe structure and FIG. 9(b) shows a multi-carrier subframestructure.

Referring to FIG. 9(a), in an FDD mode, a general wireless communicationsystem may perform data transmission or reception through one DL bandand one UL band corresponding thereto. In another specific embodiment,in a TDD mode, the wireless communication system may divide a radioframe into a UL time unit and a DL time unit in a time domain, andperform data transmission or reception through a UL/DL time unit.Referring to FIG. 9(b), three 20 MHz component carriers (CCs) can beaggregated into each of UL and DL, so that a bandwidth of 60 MHz can besupported. Each CC may be adjacent or non-adjacent to one another in thefrequency domain. FIG. 9(b) shows a case where the bandwidth of the ULCC and the bandwidth of the DL CC are the same and symmetric, but thebandwidth of each CC can be determined independently. In addition,asymmetric carrier aggregation with different number of UL CCs and DLCCs is possible. A DL/UL CC allocated/configured to a specific UEthrough RRC may be called as a serving DL/UL CC of the specific UE.

The base station may perform communication with the UE by activatingsome or all of the serving CCs of the UE or deactivating some CCs. Thebase station can change the CC to be activated/deactivated, and changethe number of CCs to be activated/deactivated. If the base stationallocates a CC available for the UE as to be cell-specific orUE-specific, at least one of the allocated CCs can be deactivated,unless the CC allocation for the UE is completely reconfigured or the UEis handed over. One CC that is not deactivated by the UE is called as aPrimary CC (PCC) or a primary cell (PCell), and a CC that the basestation can freely activate/deactivate is called as a Secondary CC (SCC)or a secondary cell (SCell).

Meanwhile, 3GPP NR uses the concept of a cell to manage radio resources.A cell is defined as a combination of DL resources and UL resources,that is, a combination of DL CC and UL CC. A cell may be configured withDL resources alone, or a combination of DL resources and UL resources.When the carrier aggregation is supported, the linkage between thecarrier frequency of the DL resource (or DL CC) and the carrierfrequency of the UL resource (or UL CC) may be indicated by systeminformation. The carrier frequency refers to the center frequency ofeach cell or CC. A cell corresponding to the PCC is referred to as aPCell, and a cell corresponding to the SCC is referred to as an SCell.The carrier corresponding to the PCell in the DL is the DL PCC, and thecarrier corresponding to the PCell in the UL is the UL PCC. Similarly,the carrier corresponding to the SCell in the DL is the DL SCC and thecarrier corresponding to the SCell in the UL is the UL SCC. According toUE capability, the serving cell(s) may be configured with one PCell andzero or more SCells. In the case of UEs that are in the RRC_CONNECTEDstate but not configured for carrier aggregation or that do not supportcarrier aggregation, there is only one serving cell configured only withPCell.

As mentioned above, the term “cell” used in carrier aggregation isdistinguished from the term “cell” which refers to a certaingeographical area in which a communication service is provided by onebase station or one antenna group. That is, one component carrier mayalso be referred to as a scheduling cell, a scheduled cell, a primarycell (PCell), a secondary cell (SCell), or a primary SCell (PScell).However, in order to distinguish between a cell referring to a certaingeographical area and a cell of carrier aggregation, in the presentdisclosure, a cell of a carrier aggregation is referred to as a CC, anda cell of a geographical area is referred to as a cell.

FIG. 10 is a diagram showing an example in which a cross carrierscheduling technique is applied. When cross carrier scheduling is set,the control channel transmitted through the first CC may schedule a datachannel transmitted through the first CC or the second CC using acarrier indicator field (CIF). The CIF is included in the DCI. In otherwords, a scheduling cell is set, and the DL grant/UL grant transmittedin the PDCCH area of the scheduling cell schedules the PDSCH/PUSCH ofthe scheduled cell. That is, a search area for the plurality ofcomponent carriers exists in the PDCCH area of the scheduling cell. APCell may be basically a scheduling cell, and a specific SCell may bedesignated as a scheduling cell by an upper layer.

In the embodiment of FIG. 10, it is assumed that three DL CCs aremerged. Here, it is assumed that DL component carrier #0 is DL PCC (orPCell), and DL component carrier #1 and DL component carrier #2 are DLSCCs (or SCell). In addition, it is assumed that the DL PCC is set tothe PDCCH monitoring CC. When cross-carrier scheduling is not configuredby UE-specific (or UE-group-specific or cell-specific) higher layersignaling, a CIF is disabled, and each DL CC can transmit only a PDCCHfor scheduling its PDSCH without the CIF according to an NR PDCCH rule(non-cross-carrier scheduling, self-carrier scheduling). Meanwhile, ifcross-carrier scheduling is configured by UE-specific (orUE-group-specific or cell-specific) higher layer signaling, a CIF isenabled, and a specific CC (e.g., DL PCC) may transmit not only thePDCCH for scheduling the PDSCH of the DL CC A using the CIF but also thePDCCH for scheduling the PDSCH of another CC (cross-carrier scheduling).On the other hand, a PDCCH is not transmitted in another DL CC.Accordingly, the UE monitors the PDCCH not including the CIF to receivea self-carrier scheduled PDSCH depending on whether the cross-carrierscheduling is configured for the UE, or monitors the PDCCH including theCIF to receive the cross-carrier scheduled PDSCH.

On the other hand, FIGS. 9 and 10 illustrate the subframe structure ofthe 3GPP LTE-A system, and the same or similar configuration may beapplied to the 3GPP NR system. However, in the 3GPP NR system, thesubframes of FIGS. 9 and 10 may be replaced with slots.

FIG. 11 illustrates a code block group (CBG) configuration and timefrequency resource mapping thereof according to an embodiment of thepresent invention. More specifically, FIG. 11(a) illustrates anembodiment of a CBG configuration included in one transport block (TB),and FIG. 11(b) illustrates a time-frequency resource mapping of the CBGconfiguration.

A channel code defines the maximum supported length. For example, themaximum supported length of the turbo code used in 3GPP LTE (-A) is 6144bits. However, the length of a transport block (TB) transmitted on thePDSCH may be longer than 6144 bits. If the length of the TB is longerthan the maximum supported length, the TB may be divided into codeblocks (CBs) having a maximum length of 6144 bits. Each CB is a unit inwhich channel coding is performed. Additionally, for efficientretransmission, several CB s may be grouped to configure one CBG. The UEand the base station require information on how the CBG is configured.

The CBG and the CB within the TB may be configured according to variousembodiments. According to an embodiment, the number of available CBGsmay be determined as a fixed value, or may be configured with RRCconfiguration information between the base station and the UE. In thiscase, the number of CBs is determined with the length of the TB, and theCBG may be configured depending on the information on the determinednumber. According to another embodiment, the number of CB s to beincluded in one CBG may be determined as a fixed value, or may beconfigured with RRC configuration information between the base stationand the UE. In this case, if the number of CBs is determined with thelength of the TB, the number of the CBGs may be configured depending onthe information on the number of CBs per CBG.

Referring to the embodiment of FIG. 11(a), one TB may be divided intoeight CBs. Eight CBs may be grouped into four CBGs again. The mappingrelationship between the CBs and the CBGs (or CBG configuration) may beconfigured as static between the base station and the UE, or may beestablished as semi-static with RRC configuration information. Accordingto another embodiment, the mapping relationship may be configuredthrough dynamic signaling. When the UE receives the PDCCH transmitted bythe base station, the UE may directly or indirectly identify the mappingrelationship between the CB and the CBG (or CBG configuration) throughexplicit information and/or implicit information. One CBG may includeonly one CB, or may include all CBs constituting one TB. For reference,the techniques presented in the embodiments of the present invention maybe applied regardless of the configuration of the CB and the CBG.

Referring to FIG. 11(b), CBGs constituting one TB are mapped totime-frequency resources for which the PDSCH is scheduled. According toan embodiment, each of the CBGs may be allocated first on the frequencyaxis and then extended on the time axis. When a PDSCH consisting of oneTB including four CBGs is allocated to seven OFDM symbols, CBG0 may betransmitted over the first and second OFDM symbols, CBG1 may betransmitted over the second, third, and fourth OFDM symbols, CBG2 may betransmitted over the fourth, fifth, and sixth OFDM symbols, and CBG3 maybe transmitted over the sixth and seventh OFDM symbols. Thetime-frequency mapping relationship allocated with the CBG and PDSCH maybe determined between the base station and the UE. However, the mappingrelationship illustrated in FIG. 11(b) is an embodiment for describingthe present invention, and the techniques presented in the embodiment ofthe present invention may be applied regardless of the time-frequencymapping relationship of the CBG.

FIG. 12 illustrates a procedure in which a base station performs aTB-based transmission or a CBG-based transmission, and a UE transmits aHARQ-ACK in response thereto. Referring to FIG. 12, the base station mayconfigure a transmission scheme suitable for the UE of the TB-basedtransmission and the CBG-based transmission. The UE may transmitHARQ-ACK information bit(s) according to the transmission schemeconfigured by the base station through the PUCCH or PUSCH. The basestation may configure the PDCCH to schedule the PDSCH to be transmittedto the UE. The PDCCH may schedule the TB-based transmission and/or theCBG-based transmission. For example, one TB or two TBs may be scheduledon the PDCCH. If one TB is scheduled, the UE has to feedback 1-bitHARQ-ACK. If two TBs are scheduled, a 2-bit HARQ-ACK has to be fed backfor each of the two TBs. In order to eliminate ambiguity between thebase station and the UE, a predetermined order may exist between eachinformation bit of the 2-bit HARQ-ACK and two TBs. For reference, whenthe MIMO transmission rank or layer is low, one TB may be transmitted onone PDSCH, and when the MIMO transmission rank or layer is high, two TBsmay be transmitted on one PDSCH.

The UE may transmit a 1-bit TB-based HARQ-ACK per one TB to inform thebase station whether or not the reception of each TB is successful. Inorder to generate a HARQ-ACK for one TB, the UE may check the receptionerror of the TB through a TB-CRC. When the TB-CRC for the TB issuccessfully checked, the UE generates an ACK for the HARQ-ACK of theTB. However, if a TB-CRC error for the TB occurs, the UE generates aNACK for the HARQ-ACK of the TB. The UE transmits TB-based HARQ-ACK(s)generated as described above to the base station. The base stationretransmits the TB of response with a NACK, among the TB-basedHARQ-ACK(s) received from the UE.

In addition, the UE may transmit a 1-bit CBG-based HARQ-ACK per one CBGto inform the base station whether or not the reception of each CBG issuccessful. In order to generate a HARQ-ACK for one CBG, the UE maydecode all CBs included in the CBG and check the reception error of eachCB through the CB-CRC. When the UE successfully receives all CBsconstituting one CBG (that is, when all CB-CRCs are successfullychecked), the UE generates an ACK for the HARQ-ACK of the CBG. However,when the UE does not successfully receive at least one of the CBsconstituting one CBG (that is, when at least one CB-CRC error occurs),the UE generates a NACK for the HARQ-ACK of the CBG. The UE transmitsthe CBG-based HARQ-ACK(s) generated as described above to the basestation. The base station retransmits the CBG of response with a NACK,among the CBG-based HARQ-ACK(s) received from the UB. According to anembodiment, the CB configuration of the retransmitted CBG may be thesame as the CB configuration of the previously transmitted CBG. Thelength of the CBG-based HARQ-ACK information bit(s) transmitted by theUE to the base station may be determined based on the number of CBGstransmitted through the PDSCH or the maximum number of CBGs configuredwith RRC signals.

On the other hand, even when the UE successfully receives all the CBGsincluded in the TB, a TB-CRC error for the TB may occur. In this case,the UE may perform flipping of the CBG-based HARQ-ACK in order torequest retransmission for the TB. That is, even though all CBGsincluded in the TB are successfully received, the UE may generate all ofthe CBG-based HARQ-ACK information bits as NACKs. Upon receiving theCBG-based HARQ-ACK feedback in which all HARQ-ACK information bits areNACKs, the base station retransmits all CBGs of the TB.

According to an embodiment of the present invention, CBG-based HARQ-ACKfeedback may be used for the successful transmission of the TB. The basestation may indicate the UE to transmit a CBG-based HARQ-ACK. In thiscase, a retransmission technique according to the CBG-based HARQ-ACK maybe used. The CBG-based HARQ-ACK may be transmitted through a PUCCH. Inaddition, when the UCI is configured to be transmitted through thePUSCH, the CBG-based HARQ-ACK may be transmitted through the PUSCH. Inthe PUCCH, the configuration of the HARQ-ACK resource may be configuredthrough an RRC signal. In addition, an actually transmitted HARQ-ACKresource may be indicated through a PDCCH scheduling a PDSCH transmittedbased on the CBG. The UE may transmit HARQ-ACK(s) for whether or not thereception of transmitted CBGs is transmitted, through one PUCCH resourceindicated through the PDCCH among PUCCH resources configured with RRC.

The base station may identify whether the UE has successfully receivedthe CBG(s) transmitted to the UE through CBG-based HARQ-ACK feedback ofthe UE. That is, through the HARQ-ACK for each CBG received from the UE,the base station may recognize the CBG(s) that the UE has successfullyreceived and the CBG(s) that the UE has failed to receive. The basestation may perform CBG retransmission based on the received CBG-basedHARQ-ACK. More specifically, the base station may bundle and retransmitonly the CBG(s) of HARQ-ACKs of response with failure, in one TB. Inthis case, the CBG(s) for which the HARQ-ACKs is responded withsuccessful reception are excluded from retransmission. The base stationmay schedule the retransmitted CBG(s) as one PDSCH and transmit it tothe UE.

<Communication Method in Unlicensed Band>

FIG. 13 illustrates a New Radio-Unlicensed (NR-U) service environment.

Referring to FIG. 13, a service environment in which NR technology 11 inthe existing licensed band and NR-Unlicensed (NR-U), i.e., NR technology12 in the unlicensed band may be provide to the user. For example, inthe NR-U environment, NR technology 11 in the licensed band and the NRtechnology 12 in the unlicensed band may be integrated usingtechnologies such as carrier aggregation which may contribute to networkcapacity expansion. In addition, in an asymmetric traffic structure withmore downlink data than uplink data, NR-U can provide an NR serviceoptimized for various needs or environments. For convenience, the NRtechnology in the licensed band is referred to as NR-L (NR-Licensed),and the NR technology in the unlicensed band is referred to as NR-U(NR-Unlicensed).

FIG. 14 illustrates a deployment scenario of a user equipment and a basestation in an NR-U service environment. A frequency band targeted by theNR-U service environment has short radio communication range due to thehigh frequency characteristics. Considering this, the deploymentscenario of the user equipment and the base station may be an overlaymodel or a co-located model in an environment in which coexist theexisting NR-L service and NR-U service.

In the overlay model, a macro base station may perform wirelesscommunication with an X UE and an X′ UE in a macro area (32) by using alicensed carrier and be connected with multiple radio remote heads(RRHs) through an X2 interface. Each RRH may perform wirelesscommunication with an X UE or an X′ UE in a predetermined area (31) byusing an unlicensed carrier. The frequency bands of the macro basestation and the RRH are different from each other not to interfere witheach other, but data needs to be rapidly exchanged between the macrobase station and the RRH through the X2 interface in order to use theNR-U service as an auxiliary downlink channel of the NR-L servicethrough the carrier aggregation.

In the co-located model, a pico/femto base station may perform thewireless communication with a Y UE by using both the licensed carrierand the unlicensed carrier. However, it may be limited that thepico/femto base station uses both the NR-L service and the NR-U serviceto downlink transmission. A coverage (33) of the NR-L service and acoverage (34) of the NR-U service may be different according to thefrequency band, transmission power, and the like.

When NR communication is performed in the unlicensed band, conventionalequipments (e.g., wireless LAN (Wi-Fi) equipments) which performcommunication in the corresponding unlicensed band may not demodulate anNR-U message or data. Therefore, conventional equipments determine theNR-U message or data as a kind of energy to perform an interferenceavoidance operation by an energy detection technique. That is, whenenergy corresponding to the NR-U message or data is lower than −62 dBmor certain energy detection (ED) threshold value, the wireless LANequipments may perform communication by disregarding the correspondingmessage or data. As a result, that user equipment which performs the NRcommunication in the unlicensed band may be frequently interfered by thewireless LAN equipments.

Therefore, a specific frequency band needs to be allocated or reservedfor a specific time in order to effectively implement an NR-Utechnology/service. However, since peripheral equipments which performcommunication through the unlicensed band attempt access based on theenergy detection technique, there is a problem in that an efficient NR-Uservice is difficult. Therefore, a research into a coexistence schemewith the conventional unlicensed band device and a scheme forefficiently sharing a radio channel needs to be preferentially made inorder to settle the NR-U technology. That is, a robust coexistencemechanism in which the NR-U device does not influence the conventionalunlicensed band device needs to be developed.

FIG. 15 illustrates a conventional communication scheme (e.g., wirelessLAN) operating in an unlicensed band. Since most devices that operate inthe unlicensed band operate based on listen-before-talk (LBT), a clearchannel assessment (CCA) technique that senses a channel before datatransmission is performed.

Referring to FIG. 15, a wireless LAN device (e.g., AP or STA) checkswhether the channel is busy by performing carrier sensing beforetransmitting data. When a predetermined strength or more of radio signalis sensed in a channel to transmit data, it is determined that thecorresponding channel is busy and the wireless LAN device delays theaccess to the corresponding channel. Such a process is referred to asclear channel evaluation and a signal level to decide whether the signalis sensed is referred to as a CCA threshold. Meanwhile, when the radiosignal is not sensed in the corresponding channel or a radio signalhaving a strength smaller than the CCA threshold is sensed, it isdetermined that the channel is idle.

When it is determined that the channel is idle, a terminal having datato be transmitted performs a backoff procedure after a defer duration(e.g., arbitration interframe space (AIFS), PCF IFS (PIFS), or thelike). The defer duration represents a minimum time when the terminalneeds to wait after the channel is idle. The backoff procedure allowsthe terminal to further wait for a predetermined time after the deferduration. For example, the terminal stands by while decreasing a slottime for slot times corresponding to a random number allocated to theterminal in the contention window (CW) during the channel is idle, and aterminal that completely exhausts the slot time may attempt to accessthe corresponding channel.

When the terminal successfully accesses the channel, the terminal maytransmit data through the channel. When the data is successfullytransmitted, a CW size (CWS) is reset to an initial value (CWmin). Onthe contrary, when the data is unsuccessfully transmitted, the CWSincreases twice. As a result, the terminal is allocated with a newrandom number within a range which is twice larger than a previousrandom number range to perform the backoff procedure in a next CW. Inthe wireless LAN, only an ACK is defined as receiving responseinformation to the data transmission. Therefore, when the ACK isreceived with respect to the data transmission, the CWS is reset to theinitial value and when feed-back information is not received withrespect to the data transmission, the CWS increases twice.

As described above, since the existing communication in the unlicensedband mostly operates based on LBT, a channel access in the NR-U systemalso performs LBT for coexistence with existing devices. Specifically,the channel access method on the unlicensed band in the NR may beclassified into the following four categories according to thepresence/absence of LBT/application method.

-   -   Category 1: No LBT    -   The Tx entity does not perform the LBT procedure for        transmission.    -   Category 2: LBT without Random Backoff    -   The Tx entity senses whether a channel is idle during a first        interval without random backoff to perform a transmission. That        is, the Tx entity may perform a transmission through the channel        immediately after the channel is sensed to be idle during the        first interval. The first interval is an interval of a        predetermined length immediately before the Tx entity performs        the transmission. According to an embodiment, the first interval        may be an interval of 25 μs length, but the present invention is        not limited thereto.    -   Category 3: LBT Performing Random Backoff Using CW of Fixed Size    -   The Tx entity obtains a random value within the CW of the fixed        size, sets it to an initial value of a backoff counter (or        backoff timer) N, and performs backoff by using the set backoff        counter N. That is, in the backoff procedure, the Tx entity        decreases the backoff counter by 1 whenever the channel is        sensed to be idle for a predetermined slot period. Here, the        predetermined slot period may be 9 μs, but the present invention        is not limited thereto. The backoff counter N is decreased by 1        from the initial value, and when the value of the backoff        counter N reaches 0, the Tx entity may perform the transmission.        Meanwhile, in order to perform backoff, the Tx entity first        senses whether the channel is idle during a second interval        (that is, a defer duration T_(d)). According to an embodiment of        the present invention, the Tx entity may sense (determine)        whether the channel is idle during the second interval,        according to whether the channel is idle for at least some        period (e.g., one slot period) within the second interval. The        second interval may be set based on the channel access priority        class of the Tx entity, and consists of a period of 16 μs and m        consecutive slot periods. Here, m is a value set according to        the channel access priority class. The Tx entity performs        channel sensing to decrease the backoff counter when the channel        is sensed to be idle during the second interval. On the other        hand, when the channel is sensed to be busy during the backoff        procedure, the backoff procedure is stopped. After stopping the        backoff procedure, the Tx entity may resume backoff when the        channel is sensed to be idle for an additional second interval.        In this way, the Tx entity may perform the transmission when the        channel is idle during the slot period of the backoff counter N,        in addition to the second interval. In this case, the initial        value of the backoff counter N is obtained within the CW of the        fixed size.    -   Category 4: LBT Performing Random Backoff by Using CW of        Variable Size    -   The Tx entity obtains a random value within the CW of a variable        size, sets the random value to an initial value of a backoff        counter (or backoff timer) N, and performs backoff by using the        set backoff counter N. More specifically, the Tx entity may        adjust the size of the CW based on HARQ-ACK information for the        previous transmission, and the initial value of the backoff        counter N is obtained within the CW of the adjusted size. A        specific process of performing backoff by the Tx entity is as        described in Category 3. The Tx entity may perform the        transmission when the channel is idle during the slot period of        the backoff counter N, in addition to the second interval. In        this case, the initial value of the backoff counter N is        obtained within the CW of the variable size.

In the above Category 1 to Category 4, the Tx entity may be a basestation or a UE. According to an embodiment of the present invention, afirst type channel access may refer to a Category 4 channel access, anda second type channel access may refer to a Category 2 channel access.

FIG. 16 illustrates a channel access procedure based on Category 4 LBTaccording to an embodiment of the present invention.

In order to perform the channel access, first, the Tx entity performschannel sensing for the defer duration T_(d) (step S302). According toan embodiment of the present invention, the channel sensing for a deferduration T_(d) in step S302 may be performed through channel sensing forat least a portion of the defer duration T_(d). For example, the channelsensing for the defer duration T_(d) may be performed through thechannel sensing during one slot period within the defer duration T_(d).The Tx entity checks whether the channel is idle through the channelsensing for the defer duration T_(d) (step S304). If the channel issensed to be idle for the defer duration T_(d), the Tx entity proceedsto step S306. If the channel is not sensed to be idle for the deferduration T_(d) (that is, sensed to be busy), the Tx entity returns tostep S302. The Tx entity repeats steps S302 to S304 until the channel issensed to be idle for the defer duration T_(d). The defer duration T_(d)may be set based on the channel access priority class of the Tx entity,and consists of a period of 16 μs and m consecutive slot periods. Here,m is a value set according to the channel access priority class.

Next, the Tx entity obtains a random value within a predetermined CW,sets the random value to the initial value of the backoff counter (orbackoff timer) N (step S306), and proceeds to step S308. The initialvalue of the backoff counter N is randomly selected from values between0 and CW. The Tx entity performs the backoff procedure by using the setbackoff counter N. That is, the Tx entity performs the backoff procedureby repeating steps S308 to S316 until the value of the backoff counter Nreaches 0. Meanwhile, FIG. 16 illustrates that step S306 is performedafter the channel is sensed to be idle for the defer duration T_(d), butthe present invention is not limited thereto. That is, step S306 may beperformed independently of steps S302 to S304, and may be performedprior to steps S302 to S304. When step S306 is performed prior to stepsS302 to S304, if the channel is sensed to be idle for the defer durationT_(d) by steps S302 to S304, the Tx entity proceeds to step S308.

In step S308, the Tx entity checks whether the value of the backoffcounter N is 0. If the value of the backoff counter N is 0, the Txentity proceeds to step S320 to perform a transmission. If the value ofthe backoff counter N is not 0, the Tx entity proceeds to step S310. Instep S310, the Tx entity decreases the value of the backoff counter Nby 1. According to an embodiment, the Tx entity may selectively decreasethe value of the backoff counter by 1 in the channel sensing process foreach slot. In this case, step S310 may be skipped at least once by theselection of the Tx entity. Next, the Tx entity performs channel sensingfor an additional slot period (step S312). The Tx entity checks whetherthe channel is idle through the channel sensing for the additional slotperiod (step S314). If the channel is sensed to be idle for theadditional slot period, the Tx entity returns to step S308. In this way,the Tx entity may decrease the backoff counter by 1 whenever the channelis sensed to be idle for a predetermined slot period. Here, thepredetermined slot period may be 9 μs, but the present invention is notlimited thereto.

In step S314, if the channel is not sensed to be idle for the additionalslot period (that is, sensed to be busy), the Tx entity proceeds to stepS316. In step S316, the Tx entity checks whether the channel is idle forthe additional defer duration T_(d). According to an embodiment of thepresent invention, the channel sensing in step S316 may be performed inunits of slots. That is, the Tx entity checks whether the channel issensed to be idle during all slot periods of the additional deferduration T_(d). When the busy slot is detected within the additionaldefer duration T_(d), the Tx entity immediately restarts step S316. Whenthe channel is sensed to be idle during all slot periods of theadditional defer duration T_(d), the Tx entity returns to step S308.

On the other hand, if the value of the backoff counter N is 0 in thecheck of step S308, the Tx entity performs the transmission (step S320).The Tx entity receives a HARQ-ACK feedback corresponding to thetransmission (step S322). The Tx entity may check whether the previoustransmission is successful through the received HARQ-ACK feedback. Next,the Tx entity adjusts the CW size for the next transmission based on thereceived HARQ-ACK feedback (step S324).

As described above, after the channel is sensed to be idle for the deferduration T_(d), the Tx entity may perform the transmission when thechannel is idle for N additional slot periods. As described above, theTx entity may be a base station or a UE, and the channel accessprocedure of FIG. 16 may be used for downlink transmission of the basestation and/or uplink transmission of the UE.

Hereinafter, a method for adaptively adjusting a CWS when accessing achannel in an unlicensed band is presented. The CWS may be adjustedbased on UE (User Equipment) feedback, and UE feedback used for CWSadjustment may include the HARQ-ACK feedback and CQI/PMI/RI. In thepresent invention, a method for adaptively adjusting a CWS based on theHARQ-ACK feedback is presented. The HARQ-ACK feedback includes at leastone of ACK, NACK, DTX, and NACK/DTX.

As described above, the CWS is adjusted based on ACK even in a wirelessLAN system. When the ACK feedback is received, the CWS is reset to theminimum value (CWmin), and when the ACK feedback is not received, theCWS is increased. However, in a cellular system, a CWS adjustment methodin consideration of multiple access is required.

First, for the description of the present invention, terms are definedas follows.

-   -   Set of HARQ-ACK feedback values (i.e., HARQ-ACK feedback set):        refers to HARQ-ACK feedback value(s) used for CWS        update/adjustment. The HARQ-ACK feedback set is decoded at a        time when the CWS is determined and corresponds to available        HARQ-ACK feedback values. The HARQ-ACK feedback set includes        HARQ-ACK feedback value(s) for one or more DL (channel)        transmissions (e.g., PDSCH) on an unlicensed band carrier (e.g.,        Scell, NR-U cell). The HARQ-ACK feedback set may include        HARQ-ACK feedback value(s) for a DL (channel) transmission        (e.g., PDSCH), for example, a plurality of HARQ-ACK feedback        values fed back from a plurality of UEs. The HARQ-ACK feedback        value may indicate reception response information for the code        block group (CBG) or the transport block (TB), and may indicate        any one of ACK, NACK, DTX, or NACK/DTX. Depending on the        context, the HARQ-ACK feedback value may be mixed with terms        such as a HARQ-ACK value, a HARQ-ACK information bit, and a        HARQ-ACK response.    -   Reference window: refers to a time interval in which a DL        transmission (e.g., PDSCH) corresponding to the HARQ-ACK        feedback set is performed in an unlicensed band carrier (e.g.,        Scell, NR-U cell). A reference window may be defined in units of        slots or subframes according to embodiments. The reference        window may indicate one or more specific slots (or subframes).        According to an embodiment of the present invention, the        specific slot (or reference slot) may include a start slot of        the most recent DL transmission burst in which at least some        HARQ-ACK feedback is expected to be available.

FIG. 17 illustrates an embodiment of a method of adjusting a contentionwindow size (CWS) based on HARQ-ACK feedback. In the embodiment of FIG.17, the Tx entity may be a base station and the Rx entity may be a UE,but the present invention is not limited thereto. In addition, althoughthe embodiment of FIG. 17 assumes a channel access procedure for the DLtransmission by the base station, at least some configurations may beapplied to a channel access procedure for the UL transmission by the UE.

Referring to FIG. 17, the Tx entity transmits the n-th DL transmissionburst on an unlicensed band carrier (e.g., Scell, NR-U cell) (stepS402), and then if an additional DL transmission is required, the Txentity may transmit the (n+1)-th DL transmission burst based on the LBTchannel access (step S412). Here, the transmission burst indicates atransmission through one or more adjacent slots (or subframes). FIG. 17illustrates a channel access procedure and a CWS adjustment method basedon the aforementioned first type channel access (that is, Category 4channel access).

First, the Tx entity receives a HARQ-ACK feedback corresponding to thePDSCH transmission(s) on an unlicensed band carrier (e.g., Scell, NR-Ucell) (step S404). The HARQ-ACK feedback used for CWS adjustmentincludes a HARQ-ACK feedback corresponding to the most recent DLtransmission burst (that is, n-th DL transmission burst) on theunlicensed band carrier. More specifically, the HARQ-ACK feedback usedfor CWS adjustment includes a HARQ-ACK feedback corresponding to thePDSCH transmission on the reference window within the most recent DLtransmission burst. The reference window may indicate one or morespecific slots (or subframes). According to an embodiment of the presentinvention, the specific slot (or reference slot) includes a start slotof the most recent DL transmission burst in which at least some HARQ-ACKfeedback is expected to be available.

When the HARQ-ACK feedback is received, a HARQ-ACK value is obtained foreach transport block (TB). The HARQ-ACK feedback includes at least oneof a TB-based HARQ-ACK bit sequence and a CBG-based HARQ-ACK. When theHARQ-ACK feedback is the TB-based HARQ-ACK bit sequence, one HARQ-ACKinformation bit is obtained per TB. On the other hand, when the HARQ-ACKfeedback is the CBG-based HARQ-ACK bit sequence, N HARQ-ACK informationbit(s) are obtained per TB. Here, N is the maximum number of CBGs per TBconfigured in the Rx entity of the PDSCH transmission. According to anembodiment of the present invention, HARQ-ACK value(s) for each TB maybe determined with the HARQ-ACK information bit(s) for each TB of theHARQ-ACK feedback for CWS determination. More specifically, when theHARQ-ACK feedback is the TB-based HARQ-ACK bit sequence, one HARQ-ACKinformation bit of the TB is determined as the HARQ-ACK value. However,when the HARQ-ACK feedback is the CBG-based HARQ-ACK bit sequence, oneHARQ-ACK value may be determined based on N HARQ-ACK information bit(s)corresponding to CBGs included in the TB.

Next, the Tx entity adjusts the CWS based on the HARQ-ACK valuesdetermined in step S404 (step S406). That is, the Tx entity determinesthe CWS based on the HARQ-ACK value(s) determined with the HARQ-ACKinformation bit(s) for each TB of the HARQ-ACK feedback. Morespecifically, the CWS may be adjusted based on the ratio of NACKs amongHARQ-ACK value(s). First, variables may be defined as follows.

-   -   p: Priority class value    -   CW_min_p: Predetermined CWS minimum value of priority class p    -   CW_max_p: Predetermined CWS maximum value of priority class p    -   CW_p: CWS for transmission of priority class p. CW_p is set to        any one of a plurality of CWS values between CW_min_p and        CW_max_p included in the allowed CWS set of the priority class        p.

According to an embodiment of the present invention, the CWS may bedetermined according to the following steps.

Step A-1) For every priority class p, CW_p is set to CW_min_p. In thiscase, the priority class p includes {1, 2, 3, 4}.

Step A-2) When the ratio of NACKs to HARQ-ACK values for the PDSCHtransmission(s) of the reference window k is Z % or more, CW_p isincreased to the next highest allowed value for every priority class p(further, Step A-2 remains). Otherwise, Step A proceeds to Step A-1.Here, Z is a predetermined integer in the range of 0<=Z<=100, andaccording to an embodiment, it may be set to one of {30, 50, 70, 80,100}.

Here, the reference window k includes the start slot (or subframe) ofthe most recent transmission by the Tx entity. In addition, thereference window k is a slot (or subframe) in which at least some of theHARQ-ACK feedbacks is expected to be possible. If CW_p=CW_max_p, thenext highest allowed value for CW_p adjustment is CW_max_p.

Next, the Tx entity selects a random value within the CWS determined instep S406 and sets the random value to the initial value of the backoffcounter N (step S408). The Tx entity performs backoff by using the setbackoff counter N (step S410). That is, the Tx entity may decrease thebackoff counter by 1 for each slot period in which the channel is sensedto be idle. When the value of the backoff counter reaches 0, the Txentity may transmit the (n+1)-th DL transmission burst in the channel(step S412).

Meanwhile, in the above-described CWS adjustment process, determinationhas to be made as to whether not only ACK and NACK but also DTX orNACK/DTX are considered together among HARQ-ACK feedbacks. According toan embodiment of the present invention, depending on whether thetransmission in the unlicensed band is based on self-carrier schedulingor cross-carrier scheduling, determination may be made as to whether DTXor NACK/DTX is considered together in the CWS adjustment process.

In self-carrier scheduling, a DL transmission (e.g., PDSCH) on theunlicensed band carrier is scheduled through the control channel (e.g.,(E)PDCCH) transmitted on the same unlicensed band carrier. Here, sincethe DTX indicates a failure of the DL transmission by a hidden node orthe like in the unlicensed band carrier, it may be used for CWSadjustment together with NACK. In addition, DTX is one of the methods inwhich the UE informs the base station that the UE fails to decode thecontrol channel even though the base station transmits, to the UE, thecontrol channel including scheduling information (e.g., (E)PDCCH). DTXmay be determined only by the HARQ-ACK feedback value, or may bedetermined taking into account the HARQ-ACK feedback value and theactual scheduling situation. According to an embodiment of the presentinvention, DTX and NACK/DTX may be counted as NACK for CWS adjustment inthe self-carrier scheduling situation. That is, when the ratio of thesum of NACK, DTX, and NACK/DTX to HARQ-ACK values for the PDSCHtransmission(s) of the reference window k is equal to or greater than Z%, the CWS is increased to the next highest allowed value. Otherwise,the CWS is reset to the minimum value.

In cross-carrier scheduling, a DL transmission (e.g., PDSCH) on theunlicensed band carrier may be scheduled through the control channel(e.g., (E)PDCCH) transmitted on the licensed band carrier. In this case,since the DTX feedback is used to determine the decoding situation ofthe UE for the control channel transmitted on the licensed band carrier,it is not helpful to adaptively adjust the CWS for a channel access inthe unlicensed band. Therefore, according to an embodiment of thepresent invention, DTX may be ignored for CWS determination in thecross-carrier scheduling situation from the licensed band. That is, forCWS adjustment, among HARQ-ACK value(s), only ACK and NACK may beconsidered for calculating the ratio of NACK, or only ACK, NACK andNACK/DTX may be considered for calculating the ratio of NACK. Therefore,when calculating the ratio of the NACK, DTX may be excluded.

FIG. 18 is a block diagram showing the configurations of a UE and a basestation according to an embodiment of the present invention. In anembodiment of the present invention, the UE may be implemented withvarious types of wireless communication devices or computing devicesthat are guaranteed to be portable and mobile. The UE may be referred toas a User Equipment (UE), a Station (STA), a Mobile Subscriber (MS), orthe like. In addition, in an embodiment of the present invention, thebase station controls and manages a cell (e.g., a macro cell, a femtocell, a pico cell, etc.) corresponding to a service area, and performsfunctions of a signal transmission, a channel designation, a channelmonitoring, a self diagnosis, a relay, or the like. The base station maybe referred to as next Generation NodeB (gNB) or Access Point (AP).

As shown in the drawing, a UE 100 according to an embodiment of thepresent disclosure may include a processor 110, a communication module120, a memory 130, a user interface 140, and a display unit 150.

First, the processor 110 may execute various instructions or programsand process data within the UE 100. In addition, the processor 100 maycontrol the entire operation including each unit of the UE 100, and maycontrol the transmission/reception of data between the units. Here, theprocessor 110 may be configured to perform an operation according to theembodiments described in the present invention. For example, theprocessor 110 may receive slot configuration information, determine aslot configuration based on the slot configuration information, andperform communication according to the determined slot configuration.

Next, the communication module 120 may be an integrated module thatperforms wireless communication using a wireless communication networkand a wireless LAN access using a wireless LAN. For this, thecommunication module 120 may include a plurality of network interfacecards (NICs) such as cellular communication interface cards 121 and 122and an unlicensed band communication interface card 123 in an internalor external form. In the drawing, the communication module 120 is shownas an integral integration module, but unlike the drawing, each networkinterface card can be independently arranged according to a circuitconfiguration or usage.

The cellular communication interface card 121 may transmit or receive aradio signal with at least one of the base station 200, an externaldevice, and a server by using a mobile communication network and providea cellular communication service in a first frequency band based on theinstructions from the processor 110. According to an embodiment, thecellular communication interface card 121 may include at least one NICmodule using a frequency band of less than 6 GHz. At least one NICmodule of the cellular communication interface card 121 mayindependently perform cellular communication with at least one of thebase station 200, an external device, and a server in accordance withcellular communication standards or protocols in the frequency bandsbelow 6 GHz supported by the corresponding NIC module.

The cellular communication interface card 122 may transmit or receive aradio signal with at least one of the base station 200, an externaldevice, and a server by using a mobile communication network and providea cellular communication service in a second frequency band based on theinstructions from the processor 110. According to an embodiment, thecellular communication interface card 122 may include at least one NICmodule using a frequency band of more than 6 GHz. At least one NICmodule of the cellular communication interface card 122 mayindependently perform cellular communication with at least one of thebase station 200, an external device, and a server in accordance withcellular communication standards or protocols in the frequency bands of6 GHz or more supported by the corresponding NIC module.

The unlicensed band communication interface card 123 transmits orreceives a radio signal with at least one of the base station 200, anexternal device, and a server by using a third frequency band which isan unlicensed band, and provides an unlicensed band communicationservice based on the instructions from the processor 110. The unlicensedband communication interface card 123 may include at least one NICmodule using an unlicensed band. For example, the unlicensed band may bea band of 2.4 GHz, 5 GHz, 6 GHz, 7 GHz or above 52.6 GHz. At least oneNIC module of the unlicensed band communication interface card 123 mayindependently or dependently perform wireless communication with atleast one of the base station 200, an external device, and a serveraccording to the unlicensed band communication standard or protocol ofthe frequency band supported by the corresponding NIC module.

The memory 130 stores a control program used in the UE 100 and variouskinds of data therefor. Such a control program may include a prescribedprogram required for performing wireless communication with at least oneamong the base station 200, an external device, and a server.

Next, the user interface 140 includes various kinds of input/outputmeans provided in the UE 100. In other words, the user interface 140 mayreceive a user input using various input means, and the processor 110may control the UE 100 based on the received user input. In addition,the user interface 140 may perform an output based on instructions fromthe processor 110 using various kinds of output means.

Next, the display unit 150 outputs various images on a display screen.The display unit 150 may output various display objects such as contentexecuted by the processor 110 or a user interface based on controlinstructions from the processor 110.

In addition, the base station 200 according to an embodiment of thepresent invention may include a processor 210, a communication module220, and a memory 230.

First, the processor 210 may execute various instructions or programs,and process internal data of the base station 200. In addition, theprocessor 210 may control the entire operations of units in the basestation 200, and control data transmission and reception between theunits. Here, the processor 210 may be configured to perform operationsaccording to embodiments described in the present invention. Forexample, the processor 210 may signal slot configuration and performcommunication according to the signaled slot configuration.

Next, the communication module 220 may be an integrated module thatperforms wireless communication using a wireless communication networkand a wireless LAN access using a wireless LAN. For this, thecommunication module 220 may include a plurality of network interfacecards such as cellular communication interface cards 221 and 222 and anunlicensed band communication interface card 223 in an internal orexternal form. In the drawing, the communication module 220 is shown asan integral integration module, but unlike the drawing, each networkinterface card can be independently arranged according to a circuitconfiguration or usage.

The cellular communication interface card 221 may transmit or receive aradio signal with at least one of the UE 100, an external device, and aserver by using a mobile communication network and provide a cellularcommunication service in the first frequency band based on theinstructions from the processor 210. According to an embodiment, thecellular communication interface card 221 may include at least one NICmodule using a frequency band of less than 6 GHz. The at least one NICmodule of the cellular communication interface card 221 mayindependently perform cellular communication with at least one of the UE100, an external device, and a server in accordance with the cellularcommunication standards or protocols in the frequency bands less than 6GHz supported by the corresponding NIC module.

The cellular communication interface card 222 may transmit or receive aradio signal with at least one of the UE 100, an external device, and aserver by using a mobile communication network and provide a cellularcommunication service in the second frequency band based on theinstructions from the processor 210. According to an embodiment, thecellular communication interface card 222 may include at least one NICmodule using a frequency band of 6 GHz or more. The at least one NICmodule of the cellular communication interface card 222 mayindependently perform cellular communication with at least one of the UE100, an external device, and a server in accordance with the cellularcommunication standards or protocols in the frequency bands 6 GHz ormore supported by the corresponding NIC module.

The unlicensed band communication interface card 223 transmits orreceives a radio signal with at least one of the UE 100, an externaldevice, and a server by using the third frequency band which is anunlicensed band, and provides an unlicensed band communication servicebased on the instructions from the processor 210. The unlicensed bandcommunication interface card 223 may include at least one NIC moduleusing an unlicensed band. For example, the unlicensed band may be a bandof 2.4 GHz, 5 GHz, 6 GHz, 7 GHz or above 52.6 GHz. At least one NICmodule of the unlicensed band communication interface card 223 mayindependently or dependently perform wireless communication with atleast one of the UE 100, an external device, and a server according tothe unlicensed band communication standards or protocols of thefrequency band supported by the corresponding NIC module.

FIG. 18 is a block diagram illustrating the UE 100 and the base station200 according to an embodiment of the present invention, and blocksseparately shown are logically divided elements of a device.Accordingly, the aforementioned elements of the device may be mounted ina single chip or a plurality of chips according to the design of thedevice. In addition, a part of the configuration of the UE 100, forexample, a user interface 140, a display unit 150 and the like may beselectively provided in the UE 100. In addition, the user interface 140,the display unit 150 and the like may be additionally provided in thebase station 200, if necessary.

In an NR system, a synchronization signal (SS) and a physical broadcastchannel (PBCH) may be received, and at least one of initial cell access,RRM measurement, and mobility management may be performed based on thesynchronization signal and the PBCH. A synchronization signal mayinclude a PSS and an SSS as described above. In addition, asynchronization signal and a PBCH may be called an SS/PBCH block or asynchronization signal and PBCH block (SSB).

The NR system regulates one subcarrier spacing defined for eachfrequency band so as to reduce complexity of searching for, by the UE,an SSB for initial cell access. Particularly, in a case where a below-6GHz frequency band is used, the NR system regulates use of onesubcarrier spacing among 15 KHz and 30 KHz for an SSB. In addition, in acase where an above-6 GHz frequency band is used, the NR systemregulates use of one subcarrier spacing among 120 KHz and 240 KHz for anSSB.

In a case where a wireless communication device performs channel accessin an unlicensed band, an LBT procedure may be used. Therefore, if achannel is not idle, the wireless communication device may fail inchannel access. Even when the base station performs channel access inorder to transmit an SSB, the channel access may fail. Therefore, SSBtransmission may not be performed at a position configured by the basestation. Eventually, even in a case where the base station configures,for the UE, a position at which an SSB is transmitted, so that the UE isable to assume a position at which an SSB is transmitted, the UE mayfail to receive an SSB. An SSB is periodically transmitted. Therefore,even though the UE fails to receive an SSB at one time point, the UE mayreceive an SSB after one period from the corresponding time point.However, in a case where the UE receives an SSB as described above,latency may occur in RRM measurement and measurement for a neighborcell. Eventually, latency may increase in the entire system.

In addition, an SSB is used for beam link configuration and beammanagement. Specifically, the base station transmits multiple SSBscorresponding to different SSB indexes in different time regions. The UEconfigures multiple beam links by using the multiple SSBs. The basestation performs beam sweeping. The UE may configure beam linksaccording to whether the UE has received SSBs transmitted throughdifferent beams in different time regions. If the base station fails inchannel access and thus fails to transmit SSBs, a problem in that the UEis unable to configure beam links occurs. Eventually, latency for beamlinks may increase due to channel access failure. Therefore, a method bywhich the number of SSB transmission failures is reduced, and SSBtransmission opportunities can be expanded is required.

In a case where the NR system is used in an unlicensed band, 60 KHzsubcarrier spacing may be used for SSB transmission so as to increasechannel access opportunities. 15 kHz or 30 kHz subcarrier spacing may beused for SSB transmission in a below-6 GHz licensed band. In addition,15 kHz, 30 kHz, or 60 kHz subcarrier spacing may be used for datatransmission in a below-6 GHz licensed band. In addition, 120 kHz or 240KHz subcarrier spacing may be used for SSB transmission in an above-6GHz licensed band. In addition, 60 KHz or 120 KHz subcarrier spacing maybe used for data transmission in an above-6 GHz licensed band. When theNR system is used in a below-7 GHz (e.g., lower than 7.125 GHz)unlicensed band, 15 kHz or 30 kHz subcarrier spacing which is the sameas that used in a below-6 GHz licensed band may be considered. However,if 60 KHz subcarrier spacing is used for SSB transmission in anunlicensed band, an OFDM symbol duration is ¼ of that in a case where 15kHz subcarrier spacing is used. Therefore, in a case where 60 kHzsubcarrier spacing is used for the NR system in an unlicensed band, theopportunities of transmission of SSBs and data channels in a unit ofsymbols after channel access may be increased. A time for transmissionof a reservation signal when the base station succeeds in channel accessin one OFDM symbol in a case where 60 kHz subcarrier spacing is used maybe smaller than a time for transmission of a reservation signal in acase where 15 kHz subcarrier spacing and 30 kHz subcarrier spacing areused.

In an unlicensed band of the NR system, the base station may transmit asignal including at least one SSB transmission or at least one SSB burstset transmission. An SSB burst set indicates that an SSB isconsecutively transmitted in a predetermined time interval. In thiscase, the signal may correspond to a discovery signal burst (DRS burst).The base station may transmit a DRS burst according to the followingprinciple. The base station may transmit a DRS burst such that a gap isnot included in a time interval in which the DRS burst is transmitted ina beam. The base station may transmit a DRS burst to satisfy an occupiedchannel bandwidth (OCB) condition. However, the base station maytransmit a DRS burst which does not satisfy the occupied channelbandwidth condition in some cases. In addition, the base station mayconsider a method for minimizing a channel occupancy time of a DRS burstand performing rapid channel access. For convenience of explanation, aDRS will be used instead of a DRS burst.

A DRS that is transmitted in an unlicensed band may include a PDSCHincluding SSB-associated remaining system information (RMSI), that is, asystem information block 1 (SIB1). Furthermore, a DRS may include anRMSI-CORESET which is a time and frequency resource region related totransmission of a control channel for transmitting schedulinginformation of RMSI. That is, a DRS may include a CORESET which is atime and frequency region for transmission of a PDCCH scheduling a PDCSHincluding an SIB1. In addition, a DRS may include a CSI-RS. In addition,a DRS may include a different type of signal. Specifically, a DRS mayinclude other system information (OSI) or paging. As described above,when the base station transmits a DRS in an unlicensed band, the basestation may multiplex the DRS with a physical channel or a signal. Inthis case, a method by which the base station performs channel access isproblematic. Particularly, which method the base station uses amongvarious channel access methods described above, and a method by which aparameter used for channel access is configured are problematic.Furthermore, a DRS may include transmission of an SSB or an SSB burstset.

In an embodiment of the present disclosure, in a case where the basestation multiplexes a DRS with unicast data, the base station mayperform a channel access in which a random backoff is performed using avariable-size CW, and the size of the CW is determined according to achannel access priority class, in order to perform transmission of a DRSand unicast data which are multiplexed. The UE may perform a channelaccess according to a channel access priority class of the multiplexedunicast data. Specifically, a channel access method may correspond to afirst type channel access described above.

In these embodiments, a case where the base station multiplexes a DRSwith a signal or information other than unicast data will be described.A signal or information other than unicast data may indicate a signal ora channel which is not data traffic, and thus it is impossible toconfigure a channel access priority class for the signal or the channel.A signal or information other than unicast data may include a controlmessage associated with initial access, random access, mobility, orpaging. In addition, a signal or information other than unicast data mayinclude transmission including only a reference signal. In addition, asignal or information other than unicast data may include transmissionincluding only a PDCCH. The transmission including only a PDCCH mayinclude at least one of an RACH message-4, a handover command, a groupcommon PDCCH, a short paging message, other system information (OSI),paging, and a random access response (RAR) under a random accessprocedure. In addition, a signal or information other than unicast datamay also be transmitted via a PDCCH and a PDSCH. For convenience ofexplanation, a signal or information other than unicast data will becalled non-unicast data. In addition, in the present specification, aDRS and non-unicast data being multiplexed may indicate that unicastdata is not included in corresponding transmission. In a detailedembodiment, in a case where the base station multiplexes a DRS withnon-unicast data, the base station may perform a channel access in whichonly LBT based on a single time interval is performed, in order toperform transmission of a DRS and non-unicast data which aremultiplexed. The channel access in which only LBT based on a single timeinterval is performed may be a second type channel access describedabove. The duration of the single time interval may be 25 μs or 34 μs.

In another detailed embodiment, in a case where the base stationmultiplexes a DRS with non-unicast data, the base station may perform achannel access in which a random backoff is performed using avariable-size CW, and the size of the CW is determined according to achannel access priority class, in order to perform transmission of a DRSand non-unicast data which are multiplexed. In this embodiment, it isconsidered that LBT based on a single time interval can be performedonly when the entire duration of transmission including only a DRS is 1ms or less, and a duty cycle of DRS transmission is 1/20 or less. Inthis embodiment, the base station may use a channel access priorityclass (e.g., channel access priority class #1) having the highestpriority. Therefore, the base station may assign a higher channel accesspriority to non-unicast data compared to unicast data. In addition, thebase station may use a channel access priority class having the highestpriority, and use the smallest CW size among CW sizes allowed in thechannel access priority class. In another detailed embodiment, the basestation may use a channel access priority class having the highestpriority, and use the largest CW size among CW sizes allowed in thechannel access priority class.

In another detailed embodiment, in a case where the base stationmultiplexes a DRS with non-unicast data, the base station may perform achannel access in which a random backoff is performed using a fixed sizeCW, in order to perform transmission of a DRS and non-unicast data whichare multiplexed. A channel access method may be a category-3 channelaccess described above. In this embodiment, the base station may use achannel access priority class (e.g., channel access priority class #1)having the highest priority. Therefore, the base station may assign ahigher channel access priority to non-unicast data compared to unicastdata. In addition, the base station may use a channel access priorityclass having the highest priority, and use the smallest CW size among CWsizes allowed in the channel access priority class. In another detailedembodiment, the base station may use a channel access priority classhaving the highest priority, and use the largest CW size among CW sizesallowed in the channel access priority class.

In a case where the base station transmits non-unicast data which hasnot been multiplexed with a DRS, the base station may perform a channelaccess for transmission of non-unicast data by using a channel accessmethod that is used when non-unicast data and a DRS are multiplexed.Specifically, in a case where the base station transmits non-unicastdata which has not been multiplexed with a DRS, the base station may usea channel access type and a channel access parameter that are used whennon-unicast data and a DRS are multiplexed.

In another detailed embodiment, in a case where the base stationtransmits non-unicast data which has not been multiplexed with a DRS,the base station may perform a channel access in which a random backoffis performed using a variable-size CW, and the size of the CW isdetermined according to a channel access priority class, in order toperform the transmission of non-unicast data. Specifically, a channelaccess method may correspond to a first type channel access describedabove. In this embodiment, the base station may use a channel accesspriority class (e.g., channel access priority class #1) having thehighest priority. Therefore, the base station may assign a higherchannel access priority to non-unicast data compared to unicast data. Inaddition, the base station may use a channel access priority classhaving the highest priority, and use the smallest CW size among CW sizesallowed in the channel access priority class. In another detailedembodiment, the base station may use a channel access priority classhaving the highest priority, and use the largest CW size among CW sizesallowed in the channel access priority class.

In another detailed embodiment, in a case where the base stationtransmits non-unicast data which has not been multiplexed with a DRS,the base station may perform a channel access in which a random backoffis performed using a fixed size CW, in order to perform the transmissionof non-unicast data. A channel access method may be a category-3 channelaccess described above. In this embodiment, the base station may use achannel access priority class (e.g., channel access priority class #1)having the highest priority. Therefore, the base station may assign ahigher channel access priority to non-unicast data compared to unicastdata. In addition, the base station may use a channel access priorityclass having the highest priority, and use the smallest CW size among CWsizes allowed in the channel access priority class. In another detailedembodiment, the base station may use a channel access priority classhaving the highest priority, and use the largest CW size among CW sizesallowed in the channel access priority class.

In the embodiments described above, the base station determines achannel access method for transmission of a DRS and non-unicast data orunicast data which are multiplexed, regardless of the duration of thetransmission of a DRS and non-unicast data or unicast data which aremultiplexed, and the duty cycle of DRS transmission. When the basestation determines a channel access method, the base station may assumethat transmission including only a DRS and transmission of a DRS andnon-unicast data which are multiplexed are the same. Specifically, thebase station may determine a channel access method for transmission of aDRS and non-unicast data or unicast data which are multiplexed, based onthe duration of the transmission of a DRS and non-unicast data orunicast data which are multiplexed, and the duty cycle of DRStransmission. The base station may determine a channel access method fortransmission of a DRS and non-unicast data or unicast data which aremultiplexed, based on whether the duration of the transmission of a DRSand non-unicast data or unicast data which are multiplexed is 1 ms orless, and the duty cycle of DRS transmission is 1/20 or less.

When the base station performs transmission of a DRS and non-unicastdata which are multiplexed, the base station may select one of twochannel access types according to whether both of two conditions aresatisfied, the two conditions being that the duration of thetransmission of a DRS and non-unicast data which are multiplexed is 1 msor shorter, and that the duty cycle of DRS transmission is 1/20 or less.One of the two channel access types indicates a channel access in whichonly LBT based on a single time interval is performed, and the other oneindicates a channel access in which a random backoff is performed usinga variable-size CW, and the size of the CW is determined according to achannel access priority class. In a detailed embodiment, if the durationof the transmission of a DRS and non-unicast data which are multiplexedis 1 ms or shorter, or the duty cycle of DRS transmission is 1/20 orless, the base station may perform a channel access in which only LBTbased on a single time interval is performed, in order to perform thetransmission of a DRS and non-unicast data which are multiplexed. Theduration of the single time interval may be 25 μs. In addition, the LBTbased on the single time interval may correspond to a second typechannel access described above. In another detailed embodiment, if theduration of the transmission of a DRS and non-unicast data which aremultiplexed is longer than 1 ms, or the duty cycle of DRS transmissionis larger than 1/20, the base station may perform a channel access inwhich a random backoff is performed using a variable-size CW, and thesize of the CW is determined according to a channel access priorityclass, in order to perform the transmission of a DRS and non-unicastdata which are multiplexed. In addition, the base station may select arandom channel access priority class. The base station may randomlyselect one of channel access priority classes satisfying a condition ofa MCOT length according to the duration of the transmission of a DRS andnon-unicast data which are multiplexed. The base station may use aselected channel access priority class for a channel access for thetransmission of a DRS and non-unicast data which are multiplexed. Thatis, the base station may use, for a channel access, a CW size accordingto the selected channel access priority class. For example, the basestation may use a channel access priority class (e.g., channel accesspriority class #1) having the highest priority. Therefore, the basestation may assign a higher channel access priority to non-unicast datacompared to unicast data. In addition, the base station may use achannel access priority class having the highest priority, and use thesmallest CW size among CW sizes allowed in the channel access priorityclass. In another detailed embodiment, the base station may use achannel access priority class having the highest priority, and use thelargest CW size among CW sizes allowed in the channel access priorityclass.

In the above embodiments, in a case where the base station is able todetermine whether the non-unicast data is received by the UE, andwhether the same is successfully received, the base station may adjust aCW size, based on a ratio between an ACK and an NACK. Specifically, thebase station may convert feedback information on non-unicast data, whichis received from the UE according to the reception by the UE, into anACK and an NACK, and may adjust a CW size, based on the ratio betweenthe ACK and the NACK. A channel access method in which a random backoffis performed using a variable-size CW, and the size of the CW isdetermined according to a channel access priority class may correspondto a first type channel access.

As described above, the base station and the UE may control a CW size,based on a HARQ feedback at a time of a channel access using a CW.However, the base station and the UE may be unable to expect a HARQfeedback on the entirety or a part of non-unicast data. In addition, thebase station and the UE may be unable to determine whether the UE or thebase station has received the entirety or a part of non-unicast data. Inaddition, in a case where the base station and the UE are required toperform an initial access procedure, the base station and the UE may beunable to determine an HARQ-ACK feedback with respect to a part of adownlink signal and channel and an uplink signal and channel, which areused in the initial access procedure. In addition, the base station andthe UE may not perform transmission related to a particular channelaccess priority class, and thus may be unable to determine an HARQ-ACKfeedback corresponding to transmission related to the correspondingchannel access priority class. In this case, a method for determining,by the base station and the UE, a CW to be used for a channel access ata time of transmission of a channel and a signal including the entirelyor a part of non-unicast data, on which it is impossible to expect anHARQ feedback, will be described. For convenience of explanation, thebase station is explained as a subject, but embodiments to be describedbelow may also be applied to the UE in the same way.

When the base station is unable to determine an HARQ-ACK feedbackrelated to transmission associated with a channel access priority classdetermining a CW size, the base station may perform a channel access inwhich a random backoff is performed in a CW corresponding to the channelaccess priority class. The base station may use the smallest CW sizeamong CW sizes allowed in the corresponding channel access priorityclass. In another detailed embodiment, the base station may use achannel access priority class having the highest priority, and use thelargest CW size among CW sizes allowed in the channel access priorityclass.

In addition, in a case where the base station is unable to determinewhether the UE has received the entirety or a part of non-unicast data,on which it is impossible to expect an HARQ feedback, the base stationmay perform a channel access in which a random backoff is performed in afixed CW size, in order to transmit the non-unicast data and a DRS whichare multiplexed. Specifically, the base station may use a CWcorresponding to one channel access priority class at a time of a firsttype channel access described above. In a detailed embodiment, the basestation may use one of channel access priority classes satisfying acondition of a MCOT length according to the duration of transmission ofa DRS and non-unicast data which are multiplexed, at a time of a firsttype channel access. The base station may use a channel access priorityclass having the highest priority. In a detailed embodiment, the basestation may use a channel access priority class having the highestpriority among channel access priority classes satisfying a condition ofa MCOT length according to the duration of transmission of a DRS andnon-unicast data which are multiplexed, at a time of a first typechannel access. In addition, the base station may use a channel accesspriority class having the highest priority, and use the smallest CW sizeamong CW sizes allowed in the channel access priority class. In anotherdetailed embodiment, the base station may use a channel access priorityclass having the highest priority, and use the largest CW size among CWsizes allowed in the channel access priority class.

In another detailed embodiment, in a case where the base station isunable to determine whether the UE has received the entirety or a partof non-unicast data, on which it is impossible to expect an HARQfeedback, the base station may perform a category-3 channel accessdescribed above, in order to transmit the non-unicast data and a DRSwhich are multiplexed. The base station may use a channel accesspriority class having the highest priority. The base station may use achannel access priority class having the highest priority among channelaccess priority classes satisfying a condition of a MCOT lengthaccording to the duration of transmission of a DRS and non-unicast datawhich are multiplexed. In addition, the base station may use a channelaccess priority class having the highest priority, and use the smallestCW size among CW sizes allowed in the channel access priority class. Inanother detailed embodiment, the base station may use a channel accesspriority class having the highest priority, and use the largest CW sizeamong CW sizes allowed in the channel access priority class.

In a case were the total duration of transmission including a DRS is 1ms or longer, the base station may perform multiple transmissions andmay determine a channel access method for each of multiple DRStransmissions.

If an unlicensed band such as a 5 GHz band or a 6 GHz band is used, thebase station may transmit a maximum of n number of SSBs in a DRS. Avalue of n may be 2, 4, or 8. In addition, subcarrier spacing used forDRS transmission may be 15 KHz or 30 KHz. If the subcarrier spacing is15 KHz, the duration of one slot may be 1 ms, and the number of SSBswhich can be included in the 1 ms interval may be 2. In addition, if thesubcarrier spacing is 30 KHz, the duration of one slot may be 0.5 ms,and the number of SSBs which can be included in the 1 ms interval may be4. The length of the total duration of DRS transmission having a dutycycle of 1/20 may change according to a DRS transmission periodconfiguration.

As described above, the total duration of transmission including a DRSmay be 1 ms or less, and the duty cycle of DRS transmission may be 1/20or less. In a case where the base station performs transmissionincluding only a DRS or transmission of a DRS and non-unicast data whichare multiplexed, the base station may perform a channel access in whichonly LBT based on a single time interval is performed, for correspondingtransmission. The channel access in which only LBT based on a singletime interval is performed may be a second type channel access describedabove. The total duration of transmission including a DRS may be longerthan 1 ms, and the duty cycle of DRS transmission may be larger than1/20. In a case where the base station performs transmission includingonly a DRS or transmission of a DRS and non-unicast data which aremultiplexed, the base station may perform a channel access in which arandom backoff is performed using a variable-size CW, and the size ofthe CW is determined according to a channel access priority class, inorder to perform corresponding transmission. The channel access methodin which a random backoff is performed using a variable-size CW, and thesize of the CW is determined according to a channel access priorityclass may correspond to a first type channel access.

In an embodiment of the present disclosure, a method for performing, bythe base station, LBT based on a single time interval may be used inconsideration of a characteristic of transmission including a DRS. Ifthe total duration of transmission including a DRS is larger than 1 ms,the base station may determine a channel access method in a unit of 1 msduration. Specifically, if the total duration of transmission includinga DRS is longer than 1 ms, the base station may perform multipletransmissions each having a duration of 1 ms or less, and may perform achannel access including only LBT based on a single time interval, foreach of the multiple transmissions. The base station may apply thisembodiment to only a case where the duty cycle of DRS transmission is1/20 or less. This is because, in a case of transmission performedwithout LBT, there is an ETSI regulation wherein a short control signalis required not to exceed 5% of the corresponding transmission. Throughthe above embodiments, the base station and the UE can rapidly performinitial access and RRM measurement through an SSB included in a DRStransmitted from the base station. For example, when the period of DRStransmission is configured to be 40 ms or longer, and the base stationperforms DRS transmission in a 5 ms interval configured as a DRStransmission window every minimum 40 ms period unit, the total durationof transmission including a DRS satisfying a condition that the dutycycle of DRS transmission is 1/20 or less may be 2 ms or less. The basestation may perform multiple DRS transmissions each having a duration of1 ms or less under a restriction wherein the total duration oftransmission including a DRS is 2 ms or less. The base station mayperform a second type channel access before performing each of themultiple transmissions. Through this embodiment, the base station canrapidly perform transmission of a DRS to the UE. In addition, when theperiod of DRS transmission is configured to be 80 ms or longer, and thebase station performs DRS transmission in a 5 ms interval configured asa DRS transmission window every minimum 80 ms period unit, the totalduration of transmission including a DRS satisfying a condition that theduty cycle of DRS transmission is 1/20 or less may be 4 ms or less. Thebase station may perform multiple DRS transmissions each having aduration of 1 ms or less under a restriction wherein the total durationof transmission including a DRS is 4 ms or less. The base station mayperform a second type channel access before performing each of themultiple transmissions.

In addition, if the total duration of transmission including a DRS islonger than 1 ms, and the duty cycle of DRS transmission is larger than1/20, the base station may perform a channel access in which a randombackoff is performed using a variable-size CW, and the size of the CW isdetermined according to a channel access priority class, in order toperform the transmission including a DRS. The channel access method maycorrespond to a first type channel access.

In another detailed embodiment, a partial interval of transmissionincluding a DRS may have a transmission duty cycle of 1/20 or less. Thebase station may perform a channel access in which only LBT based on asingle time interval is performed, for a partial transmission intervalof the transmission interval of transmission including a DRS, the dutycycle of which is 1/20 or less. In addition, in this embodiment, thebase station may perform multiple transmissions each having a durationof 1 ms or less, and may perform a channel access including only LBTbased on a single time interval, for each of the multiple transmissions.The channel access in which only LBT based on a single time interval isperformed may be a second type channel access. In addition, the basestation may perform a channel access in which a random backoff isperformed using a variable-size CW, and the size of the CW is determinedaccording to a channel access priority class, for the remainingtransmission interval of the transmission interval of the transmissionincluding a DRS. The channel access in which a random backoff isperformed using a variable-size CW, and the size of the CW is determinedaccording to a channel access priority class may be a first type channelaccess. For example, the period of DRS transmission may be a multiple of20 ms. Specifically, if the period of DRS transmission is 20 ms, theduration of a transmission interval in which the duty cycle of the DRStransmission is 1/20 or less is 1 ms. If the period of DRS transmissionis 40 ms, the duration of a transmission interval in which the dutycycle of the DRS transmission is 1/20 or less is 2 ms. If the period ofDRS transmission is 60 ms, the duration of a transmission interval inwhich the duty cycle of the DRS transmission is 1/20 or less is 3 ms. Ifthe period of DRS transmission is 80 ms, the duration of a transmissioninterval in which the duty cycle of the DRS transmission is 1/20 or lessis 4 ms. The base station may perform a second type channel access for apartial transmission interval of a transmission interval of transmissionincluding a DRS, the duty cycle of which is 1/20, and may perform afirst type channel access for the remaining transmission interval of thetransmission interval of the transmission including a DRS.

A maximum number of SSBs which can be included in a DRS may be 8. Thefollowing description will be given under the assumption that the numberof SSBs included in a DRS is 8. If the period of DRS transmission is 20ms, the duration of a transmission interval in which the duty cycle ofthe DRS transmission is 1/20 or less is 1 ms. Therefore, if subcarrierspacing is 15 KHz, two SSBs may be included in the transmission intervalin which the duty cycle of the DRS transmission is 1/20 or less. Thebase station may perform a second type channel access before performingfirst transmission, and if the channel access is successful, the basestation may transmit two SSBs. In addition, the base station may performa first type channel access before performing second transmission, andif the channel access is successful, the base station may transmit sixSSBs. In addition, if the period of DRS transmission is 20 ms, theduration of a transmission interval in which the duty cycle of the DRStransmission is 1/20 or less is 1 ms. Therefore, if subcarrier spacingis 30 KHz, four SSBs may be included in the transmission interval inwhich the duty cycle of the DRS transmission is 1/20 or less. The basestation may perform a second type channel access before performing firsttransmission, and if the channel access is successful, the base stationmay transmit four SSBs. In addition, the base station may perform afirst type channel access before performing second transmission, and ifthe channel access is successful, the base station may transmit fourSSBs.

If the period of DRS transmission is 40 ms, the duration of atransmission interval in which the duty cycle of the DRS transmission is1/20 or less is 2 ms. Therefore, if subcarrier spacing is 15 KHz, fourSSBs may be included in the transmission interval in which the dutycycle of the DRS transmission is 1/20 or less. The base station mayperform transmission having a duration of 1 ms twice, and may transmittwo SSBs through each transmission. The base station may perform asecond type channel access before performing first transmission, and ifthe channel access is successful, the base station may transmit twoSSBs. In addition, the base station may perform a second type channelaccess before performing second transmission, and if the channel accessis successful, the base station may transmit two SSBs. In addition, thebase station may perform a first type channel access before performingthird transmission, and if the channel access is successful, the basestation may transmit the remaining four SSBs. In addition, if the periodof DRS transmission is 40 ms, the duration of a transmission interval inwhich the duty cycle of the DRS transmission is 1/20 or less is 2 ms.Therefore, if subcarrier spacing is 30 KHz, eight SSBs may be includedin the transmission interval in which the duty cycle of the DRStransmission is 1/20 or less. The base station may perform a second typechannel access before performing first transmission, and if the channelaccess is successful, the base station may transmit four SSBs. Inaddition, the base station may perform a second type channel accessbefore performing second transmission, and if the channel access issuccessful, the base station may transmit four SSBs.

In another detailed embodiment, a partial interval of transmissionincluding a DRS may have a duration of 1 ms or less and a DRStransmission duty cycle of 1/20 or less. The base station may perform achannel access in which only LBT based on a single time interval isperformed, for the partial interval of the transmission including a DRS,which has a duty cycle of 1/20 or less and a duration of 1 ms or less.The channel access in which only LBT based on a single time interval isperformed may be a second type channel access. In addition, the basestation may perform, for the remaining transmission interval, a channelaccess in which a random backoff is performed using a variable-size CW,and the size of the CW is determined according to a channel accesspriority class. The channel access in which a random backoff isperformed using a variable-size CW, and the size of the CW is determinedaccording to a channel access priority class may be a first type channelaccess.

A maximum number of SSBs which can be included in a DRS may be 8. Thefollowing description will be given under the assumption that the numberof SSBs included in a DRS is 8.

If the period of DRS transmission is 20 ms, the duration of atransmission interval in which the duty cycle of the DRS transmission is1/20 or less is 1 ms. Therefore, if subcarrier spacing is 15 KHz, twoSSBs may be included in the transmission interval in which the dutycycle of the DRS transmission is 1/20 or less. The base station mayperform a second type channel access before performing firsttransmission, and if the channel access is successful, the base stationmay transmit two SSBs. In addition, the base station may perform a firsttype channel access before performing second transmission, and if thechannel access is successful, the base station may transmit six SSBs. Inaddition, if the period of DRS transmission is 20 ms, the duration of atransmission interval in which the duty cycle of the DRS transmission is1/20 or less is 1 ms. Therefore, if subcarrier spacing is 30 KHz, fourSSBs may be included in the transmission interval in which the dutycycle of the DRS transmission is 1/20 or less. The base station mayperform a second type channel access before performing firsttransmission, and if the channel access is successful, the base stationmay transmit four SSBs. In addition, the base station may perform afirst type channel access before performing second transmission, and ifthe channel access is successful, the base station may transmit fourSSBs.

If the period of DRS transmission is 40 ms, the duration of atransmission interval in which the duty cycle of the DRS transmission is1/20 or less is 2 ms. If subcarrier spacing is 15 KHz, two SSBs may beincluded in a transmission interval having a duration of 1 ms and a DRStransmission duty cycle of 1/20 or less. The base station may perform asecond type channel access before performing first transmission, and ifthe channel access is successful, the base station may transmit twoSSBs. In addition, the base station may perform a first type channelaccess before performing second transmission, and if the channel accessis successful, the base station may transmit the remaining six SSBs. Inaddition, if the period of DRS transmission is 40 ms, the duration of atransmission interval in which the duty cycle of the DRS transmission is1/20 or less is 2 ms. If subcarrier spacing is 30 KHz, four SSBs may beincluded in a transmission interval having a duration of 1 ms and a DRStransmission duty cycle of 1/20 or less. The base station may perform asecond type channel access before performing first transmission, and ifthe channel access is successful, the base station may transmit fourSSBs. In addition, the base station may perform a first type channelaccess before performing second transmission, and if the channel accessis successful, the base station may transmit four SSBs.

In addition, a DRS transmission window duration may be configured to beT ms. T may be a natural number of 1 or more. T may be 5 or 6.Alternatively, T may be configured to be a multiple of a minimum timeinterval in which a maximum available number of SSBs included in a DRScan be included. If the duration of a DRS transmission window is 1 ms ormore, the base station may perform a channel access in which only LBTbased on a single time interval is performed, before the last 1 ms ofthe DRS transmission window. If the DRS transmission duty cycle of thelast 1 ms of the DRS transmission window is 1/20 or less, the basestation may perform a channel access in which only LBT based on a singletime interval is performed, before the last 1 ms of the DRS transmissionwindow. The channel access in which only LBT based on a single timeinterval is performed may be a second type channel access describedabove. In addition, the base station may perform a first type channelaccess or a second type channel access before the last 1 ms of the DRStransmission window. Through these embodiments, the UE can rapidlyperform initial access and RRM measurement.

A method for configuring a CORESET in an unlicensed band and configuringa start and length indicator value (SLIV) of a PDSCH for remainingsystem information (RMSI) will be described. Specifically, a method forconfiguring the position of a symbol which can be occupied by a CORESETon which a PDCCH scheduling RMSI is transmitted, the length of a PDSCHin which RMSI is transmitted, and a start time point of a PDSCH will bedescribed with reference to FIG. 19.

FIG. 19 shows the position of OFDM symbols occupied by an SSB accordingto an embodiment of the present disclosure in a slot including 14 OFDMsymbols.

The position of OFDM symbols of SSB pattern A illustrated in FIG. 19 isthe same as the position of OFDM symbols occupied by an SSB in an NRsystem regulated by 3GPP Rel. 15. The position of OFDM symbols of SSBpattern B illustrated in FIG. 19 is changed from SSB pattern A such thatthe SSB positioned in a second half slot is shifted backwards by oneOFDM symbol size in every slot. Therefore, in SSB pattern B, an SSB ispositioned on the same OFDM symbols in a half slot, based on a half slotboundary in every slot.

A case where the first embodiment is applied to SSB pattern A will bedescribed. A first CORESET on which a PDCCH scheduling a RMSI-PDSCHassociated with a first SSB of a slot is transmitted may be configuredto occupy a first symbol and a second symbol of the slot when the firstCORESET occupies two symbols. If the first CORESET occupies only onesymbol, the first CORESET may be configured to occupy the first symbolof the slot. A second CORESET on which a PDCCH scheduling a RMSI-PDSCHassociated with a second SSB of the slot is transmitted may beconfigured to occupy a seventh symbol and an eighth symbol of the slotwhen the second CORESET occupies two symbols. If the second CORESEToccupies only one symbol, the second CORESET may be configured to occupythe seventh symbol or the eighth symbol of the slot.

A case where the third embodiment is applied to SSB pattern A will bedescribed. If a first CORESET, on which a PDCCH scheduling a RMSI-PDSCHassociated with a first SSB of a slot is transmitted, occupies twosymbols, the base station may configure the first CORESET to occupy afirst symbol and a second symbol of the slot. If the first CORESEToccupies only one symbol, the base station may configure the firstCORESET to occupy the first symbol of the slot. The second CORESET onwhich a PDCCH scheduling a RMSI-PDSCH associated with a second SSB ofthe slot is transmitted does not support a case where the second CORESEToccupies two symbols. If the second CORESET occupies only one symbol,the base station may configure the second CORESET to occupy an eighthsymbol of the slot.

A case where the second embodiment is applied to SSB pattern B will bedescribed. If a first CORESET, on which a PDCCH scheduling a RMSI-PDSCHassociated with a first SSB of a slot is transmitted, occupies twosymbols, the base station may configure the first CORESET to occupy afirst symbol and a second symbol of the slot. If the first CORESEToccupies only one symbol, the first CORESET may be configured to occupythe first symbol of the slot. If a second CORESET, on which a PDCCHscheduling a RMSI-PDSCH associated with a second SSB of the slot istransmitted, occupies only two symbols, the base station may configurethe second CORESET to occupy an eighth symbol and a ninth symbol of theslot. If the second CORESET occupies only one symbol, the base stationmay configure the second CORESET to occupy the eighth symbol of theslot.

A method for configuring a PDSCH SLIV for a RMSI-PDSCH will be describedaccording to each of the first embodiment to the third embodimentdescribed above. A precondition that the number of REs which can beincluded in each of a first half slot and a second half slot of a slotis the same may be applied.

If a RMSI-PDSCH is configured by four symbols, the symbol position ofthe RMSI-PDSCH in a slot may follow the embodiment below. According tothe first embodiment, a start symbol of an RMSI-PDSCH associated with afirst SSB of a slot may be one of a second, a third, or a fourth symbolof the slot. Alternatively, a start symbol of an RMSI-PDSCH associatedwith a second SSB of the slot may be one of an eighth, a ninth, or atenth symbol of the slot. The base station may configure the last onesymbol of the slot to be empty for an LBT gap.

According to the second embodiment, a start symbol of an RMSI-PDSCHassociated with a first SSB of a slot may be one of a second, a third,or a fourth symbol of the slot. Alternatively, a start symbol of anRMSI-PDSCH associated with a second SSB of the slot may be one of aninth, a tenth, or an eleventh symbol of the slot. An LBT gap is notconfigured for this case.

According to the third embodiment, a start symbol of an RMSI-PDSCHassociated with a first SSB of a slot may be one of a third or a fourthsymbol of the slot. Alternatively, a start symbol of an RMSI-PDSCHassociated with a second SSB of the slot may be one of a ninth or atenth symbol of the slot. The base station may configure the last onesymbol of the slot to be empty for an LBT gap.

Independently from a configuration of an SLIV of an RMSI-PDSCH accordingto each of the embodiments, if an RMSI-PDSCH is configured by foursymbols, the last one symbol of a slot may be configured to be empty foran LBT gap between slots. Regardless of the length of a CORESET, a startsymbol of an RMSI-PDSCH associated with a first SSB of a slot may be athird symbol of the slot, or a start symbol of an RMSI-PDSCH associatedwith a second SSB of the slot may be a ninth symbol or a tenth symbol ofthe slot.

If a RMSI-PDSCH is configured by five symbols, the symbol position ofthe RMSI-PDSCH in a slot may follow the embodiment below. According tothe first embodiment, a start symbol of an RMSI-PDSCH associated with afirst SSB of a slot may be one of a second or a third symbol of theslot. Alternatively, a start symbol of an RMSI-PDSCH associated with asecond SSB of the slot may be one of an eighth or a ninth symbol of theslot. The base station may configure the last one symbol of the slot tobe empty for an LBT gap.

According to the second embodiment, a start symbol of an RMSI-PDSCHassociated with a first SSB of a slot may be one of a second or a thirdsymbol of the slot. Alternatively, a start symbol of an RMSI-PDSCHassociated with a second SSB of the slot may be one of a ninth or atenth symbol of the slot. An LBT gap is not configured in this case.

According to the third embodiment, a start symbol of an RMSI-PDSCHassociated with a first SSB of a slot may be a third symbol of the slot.Alternatively, a start symbol of an RMSI-PDSCH associated with a secondSSB of the slot may be a ninth symbol of the slot. The base station mayconfigure the last one symbol of the slot to be empty for an LBT gap.

Independently from a configuration of an SLIV of an RMSI-PDSCH accordingto each of the embodiments, if an RMSI-PDSCH is configured by fivesymbols, the last one symbol of a slot may be configured to be empty foran LBT gap between slots. Regardless of the length of a CORESET, a startsymbol of an RMSI-PDSCH associated with a first SSB of a slot may be athird symbol of the slot, or a start symbol of an RMSI-PDSCH associatedwith a second SSB of the slot may be a ninth symbol of the slot.

If an RMSI-PDSCH is configured by six symbols, a start symbol of anRMSI-PDSCH in a slot may follow the embodiment below. If an RMSI-PDSCHis configured by six symbols, a CORESET may occupy only one symbol. Agap between slots is not configured for this case. Specifically, a startsymbol of an RMSI-PDSCH associated with a first SSB of a slot may be asecond symbol. Alternatively, a start symbol of an RMSI-PDSCH associatedwith a second SSB of the slot may be a ninth symbol. As described above,an LBT gap is not configured, and if an LBT gap is required to beconfigured, an RMSI-PDSCH configured by six symbols may not beconfigured. Alternatively, if an LBT gap is required to be configured,the base station may indicate only an RMSI-PDSCH configured by foursymbols or an RMSI-PDSCH configured by five symbols, and allow the UE toreceive an indicated RMSI-PDSCH.

The method and the system of the present disclosure have been describedin relation to a particular embodiment. However, some or all of elementsor operation thereof may be implemented using a computing system havinggeneric-purpose hardware architecture.

The above description of the present disclosure is made for illustrativepurposes, and those skilled in the art to which the present disclosurebelongs will be able to understand that the present disclosure may beeasily modified in other specific forms without changing the technicalspirit and essential features of the present disclosure. Therefore, itshould be understood that the above-described embodiments are exemplaryin all respects and not restrictive. For example, each element, which isdescribed as a single form, may be implemented in a distributed manner,and similarly, elements described as distributed forms may beimplemented in a combined form.

The scope of the present disclosure is shown by the following claimsrather than the above description, and all changes or modificationsderived from the meaning and scope of the claims and their equivalentsshould be construed as being included in the scope of the presentdisclosure.

1. A base station of a wireless communication system, the base stationcomprising: a communication module; and a processor configured tocontrol the communication module, wherein the processor is configured toselect one of two channel access types according to whether both of twoconditions are satisfied, when the base station performs transmission ofa DRS and non-unicast data which are multiplexed, the two conditionsbeing that a duration of the transmission of a DRS and non-unicast datawhich are multiplexed is 1 ms or shorter, and that a duty cycle of DRStransmission is 1/20 or less, and among the two channel access types, afirst type is a channel access in which a random backoff is performedusing a variable-size contention window (CW), and a size of the CW isdetermined according to a channel access priority class, and a secondtype is a channel access in which only LBT based on a single timeinterval is performed.
 2. The base station of claim 1, wherein, when theduration of the transmission of a DRS and non-unicast data which aremultiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, the processor is configured to performa channel access employing the first type in order to perform thetransmission of a DRS and non-unicast data which are multiplexed.
 3. Thebase station of claim 2, wherein, when the duration of the transmissionof a DRS and non-unicast data which are multiplexed is longer than 1 ms,or the duty cycle of the DRS transmission is larger than 1/20, theprocessor is configured to randomly select a channel access priorityclass, and applie the selected channel access priority class to thechannel access employing the first type.
 4. The base station of claim 3,wherein, when the duration of the transmission of a DRS and non-unicastdata which are multiplexed is longer than 1 ms, or the duty cycle of theDRS transmission is larger than 1/20, the processor is configured torandomly select one of channel access priority classes allowed accordingto a length of the duration of the transmission of a DRS and non-unicastdata which are multiplexed, and apply a selected channel access priorityclass to the channel access employing the first type.
 5. The basestation of claim 3, wherein, when the duration of the transmission of aDRS and non-unicast data which are multiplexed is longer than 1 ms, orthe duty cycle of the DRS transmission is larger than 1/20, theprocessor is configured to apply, to the channel access employing thefirst type, a channel access priority class having a highest priority.6. The base station of claim 1, wherein the processor is configured to:when the base station performs the transmission of a DRS and non-unicastdata which are multiplexed, through a channel access employing the firsttype, adjust the size of the CW, based on a hybrid automatic repeatrequest (HARQ)-ACK feedback related to transmission associated with thechannel access priority class determining the size of the CW; and whenthe base station is unable to determine a HARQ-ACK feedback related totransmission associated with the channel access priority classdetermining the size of the CW, perform the channel access employing thefirst type by using a smallest value among CW size values allowed forthe channel access priority class determining the size of the CW.
 7. Thebase station of claim 1, wherein, when the duration of the transmissionof a DRS and non-unicast data which are multiplexed is 1 ms or shorter,or the duty cycle of the DRS transmission is 1/20 or less, the processoris configured to perform a channel access using the second type in orderto perform the transmission of a DRS and non-unicast data which aremultiplexed.
 8. The base station of claim 7, wherein a duration of thesingle time interval is 25 μs.
 9. The base station of claim 1, whereinthe non-unicast data comprises at least one of an RACH message-4, ahandover command, a group common PDCCH, a short paging message, othersystem information (OSI), and a random access response (RAR).
 10. Amethod of operating a base station of a wireless communication system,the method comprising: when the base station performs transmission of aDRS and non-unicast data which are multiplexed, selecting one of twochannel access types according to whether both of two conditions aresatisfied, the two conditions being that a duration of the transmissionof a DRS and non-unicast data which are multiplexed is 1 ms or shorter,and that a duty cycle of DRS transmission is 1/20 or less; andperforming the transmission according to the selected channel accesstype, wherein, among the two channel access types, a first type is achannel access in which a random backoff is performed using avariable-size contention window (CW), and a size of the CW is determinedaccording to a channel access priority class, and a second type is achannel access in which only LBT based on a single time interval isperformed.
 11. The method of claim 10, wherein the performing thetransmission further comprises, when the duration of the transmission ofa DRS and non-unicast data which are multiplexed is longer than 1 ms, orthe duty cycle of the DRS transmission is larger than 1/20, performing achannel access employing the first type in order to perform thetransmission of a DRS and non-unicast data which are multiplexed. 12.The method of claim 11, wherein the performing the channel accessemploying the first type further comprises: when the duration of thetransmission of a DRS and non-unicast data which are multiplexed islonger than 1 ms, or the duty cycle of the DRS transmission is largerthan 1/20, randomly selecting a channel access priority class; andapplying the selected channel access priority class to the channelaccess employing the first type.
 13. The method of claim 12, wherein therandom selecting the channel access priority class further comprises,when the duration of the transmission of a DRS and non-unicast datawhich are multiplexed is longer than 1 ms, or the duty cycle of the DRStransmission is larger than 1/20, randomly selecting one of channelaccess priority classes allowed according to a length of the duration ofthe transmission of a DRS and non-unicast data which are multiplexed.14. The method of claim 12, wherein the random selecting the channelaccess priority class further comprises, when the duration of thetransmission of a DRS and non-unicast data which are multiplexed islonger than 1 ms, or the duty cycle of the DRS transmission is largerthan 1/20, applying, by a processor and to the channel access employingthe first type, a channel access priority class having a highestpriority.
 15. The method of claim 9, wherein the performing thetransmission further comprises: when the base station performs thetransmission of a DRS and non-unicast data which are multiplexed,through a channel access employing the first type, adjusting the size ofthe CW, based on a hybrid automatic repeat request (HARQ)-ACK feedbackrelated to transmission associated with the channel access priorityclass determining the size of the CW; and when the base station isunable to determine a HARQ-ACK feedback related to transmissionassociated with the channel access priority class determining the sizeof the CW, performing the channel access employing the first type byusing a smallest value among CW size values allowed for the channelaccess priority class determining the size of the CW.
 16. The method ofclaim 9, wherein the performing the transmission further comprises, whenthe duration of the transmission of a DRS and non-unicast data which aremultiplexed is 1 ms or shorter, or the duty cycle of the DRStransmission is 1/20 or less, performing a channel access using thesecond type in order to perform the transmission of a DRS andnon-unicast data which are multiplexed.
 17. The method of claim 16,wherein a duration of the single time interval is 25 μs.
 18. The methodof claim 9, wherein the non-unicast data comprises at least one of anRACH message-4, a handover command, a group common PDCCH, a short pagingmessage, other system information (OSI), and a random access response(RAR).